28 THE UNIVERSITY OF KANSAS PALEONTOLOGICAL CONTRIBUTIONS FIGURES 18-22. Decaschisma pentalobus (HALL) (Univ. Chicago, no. 2,554) and D. pulchellum (MILLER & DYER) (Univ. Chicago, no. 2,810), both Silurian, Indiana. 18-20. D. pentalobus, anal view, X16; aboral view <strong>of</strong> "C" ambulacrum, X16, "E" ambulacrum, X50. 21, 22. D. pulchellum, anal view, X16; "B" ambulacrum, X50. [Explanation.—An, anal opening; Bf, brachiolar facet; Bp, brachiolar pit; "C," amb.; C, canal (radial); "D," amb.; D, deltoid; Db, deltoid body; Dc, deltoid crest; D1, deltoid lip; Ds, deltoid septum; HD, hypodeltoid; Hs, hydrospire slit; L, lancet; 0, oral opening; OSp, outer side plate; R, radial; RI, radial limb; Sp, main side plate; Ss, spiracular slit; Su, superdeltoid; Sub, subdeltoid.]
BLASTOID STUDIES 29 mm. long by 2 mm. wide by 1.5 mm. deep, forming part <strong>of</strong> the summit; radial limbs overlapping deltoids. Deltoids four, lanceolate, each 2 mm. long by 1 mm. wide, not visible in side view, with a broad V-shaped lip, deep septum, and high body projected into a low coronal process, with approximately eight or nine hydrospire slits on each side <strong>of</strong> an ambulacrum, <strong>of</strong> which four or five are exposed. The slits extend to the adjacent radial limbs, parallel to the lancet plate. On the anal side there are three deltoid plates, superdeltoid, subdeltoid, and hypo-. deltoid. The broad V-shaped superdeltoid is adjacent to the oral opening, the elongate V-shaped subdeltoid resting on the internal aboral surface <strong>of</strong> the superdeltoid. The subdeltoid has two limbs that extend aborally on either side <strong>of</strong> the anal opening and partly beneath the adjacent lancet plates, folded internally into three hydrospire slits on each side, the limbs being overlapped by the adjacent radial limbs, and hydrospire slits extended to the radial limbs. The large pentagonal hypodeltoid, 1.25 mm. long by 1.75 mm. wide, visible in side view, covers parts <strong>of</strong> the subdeltoid limbs and abuts against the radial limbs. Ambulacra fi ve, short, linear, each 3 mm. long by 1 mm. wide, lancet being completely covered by side plates, <strong>of</strong> which 35 occur in 10 mm. Primary side plates subquadrangular, with subtriangular secondary side plates on bevelled abmedial-adoral corner. The surfaces <strong>of</strong> the calyx plates are ornamented with fi ne growth striae parallel to the margins. Remarks.—This species may readily be distinguished from D. pentalobus by the flaring basal circlet, not present in D. pentalobus. Occurrence.—Silurian, Waldron Shale, Waldron, Indiana. Types.—Topotypes, 2,810, 11 specimens, Washburn collection, Walker Museum, <strong>University</strong> <strong>of</strong> Chicago, Chicago, Ill. The description is based mainly on characters seen in the specimen figured on plate 1. Genus DELTOSCHISMA Fay, n. gen. Type-species, by original designation (herein).—Phaenoschisma archiaci ETHERIDGE & CARPENTER, 1882. Generic diagnosis.—Fissiculate blastoids with ten exposed hydrospire fields, four anal deltoids or a superdeltoid, two cryptodeltoids, and a hypodeltoid, a reduced number <strong>of</strong> slits on the anal side, lancet covered by large side plates, calyx steeply conical in side view, strongly pentalobate in top view. Devonian, Spain. DELTOSCHISMA ARCHIACI (Etheridge & Carpenter) Plate 1, figures 4-6; text-figs. 23-25 Phaenoschisma archiaci ETHERIDGE & CARPENTER, 1882, pp. 229- 230. Description.—Calyx calcitic, steeply conical in side view, pentagonal in top view, 13.5 mm. long by 7 mm. wide, periphery at radial lips, with vault 1 mm. long, pelvis 12.5 mm. long, and pelvic angle 30 degrees. Stem round, with preserved part 4 mm. long by 2 mm. wide. Each columnal is 0.75 mm. long, smooth, with smooth facets and small round lumen. An enlarged columnal occurs at the aboral extremity <strong>of</strong> the basal circlet, with a tripartite proximal facet, each part concave upward to fit against the convex aboral ends <strong>of</strong> the basal plates. Basal circlet steeply conical in side view, rounded in basal view, 7.5 mm. long by 6 mm. wide, enlarged at base, with the apex <strong>of</strong> a strongly triangular ridge near the geometric center <strong>of</strong> the aboral one-fourth <strong>of</strong> each basal. Radials five, each hexagonal, 7 mm. long by 3.5 mm. wide, with wide, short flaring sinus 2.5 mm. long by 2 mm. wide. In top view each radial plate appears lobed near the radial lip and a slight constriction is seen along each interradial suture, giving a slight pentalobate appearance to the calyx in top view; radials overlapping deltoids. Deltoids four, lanceolate, not visible in side view, each 1.75 mm. long by 1.5 mm. wide, with approximately eight hydrospire slits on each side <strong>of</strong> an ambulacrum, parallel to the lancet plate, and continuing aborally to the adjacent radial limbs. Approximately four hydrospire slits are exposed along the steep sinus walls, the other four being only partly exposed. The four hexagonal deltoid lips are adjacent to the oral opening and connected to the deltoid body by a low medium septum that is prominent, thus giving the appearance <strong>of</strong> eight spiracular slits around the oral opening. On the anal side there are four deltoid plates, a hexagonal superdeltoid, two thin long cryptodeltoids (mostly destroyed) on either side <strong>of</strong> the anal opening, and a pentagonal hypodeltoid (missing, but facets present) on the aboral side <strong>of</strong> the anal opening. The hypodeltoid would abut against the truncated radial limbs if preserved in place. The aboral ends <strong>of</strong> the cryptodeltoids are destroyed, but ETHERIDGE & CARPENTER (1886, p. 277) report that a reduced number <strong>of</strong> slits are present on either side <strong>of</strong> the anal opening. Thus there are ten hydrospire fi elds, the number <strong>of</strong> slits being reduced on the two anal fields; four anal deltoids occur. Ambulacra five, linear, short, each 3 mm. long by 1 mm. wide, the lancet being covered by side plates, with a total <strong>of</strong> eight side plates in each ambulacrum and 30 side plates in a space <strong>of</strong> 10 mm. Each primary side plate is subquadrangular with a secondary side plate on the abmedial-adoral corner <strong>of</strong> each, with about four main cover-plate sockets to each side plate along the main food groove and four side cover-plate sockets along each side food groove. The surfaces <strong>of</strong> calyx plates are ornamented with fine growth striae parallel to the margins. Remarks.—The genus Deltoschisma is the most primitive European blastoid known to date. It is similar to Polydeltoideus <strong>of</strong> the Silurian <strong>of</strong> North America but
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