the molluscan fauna of the alum bluff group of florida

Genus DOSINIA Scopoli
1777. Dosinia Scopoli, Introductio ad historiam naturalem
sistens genera lapidum, plantarum et animalium,
p. 398.
Type: Chama dosin Adanson = Dosinia africana
Gray. (Recent, off the coast of Senegal.)
Dall 3 describes this genus as follows:
Animal with a large arcuate foot and closely united siphons.
Complete dental formula (the posterior right cardinal, being
extremely thin, is often broken off, eroded, or obsolete)
L. oioioio.oio ,, ,. . , .,,, ,. , , , . ,
R i ioioi i i ' thick middle cardinals are often bifid or
excavated. Valves suborbicular, generally compressed, with
a long and strong ligament seated in a groove and enfolding a
heavy resilium; lunule small, impressed; escutcheon narrow,
nearly linear or absent; hinge plate broad and thick; valve
margins smooth; pallial sinus rather long and usually acute,
anterior lateral teeth nearly obsolete and usually simple;
sculpture usually of elegantly concentric grooves and inter­
spaces, sometimes raised into lamellae at the borders of the
lunule and escutcheon, crossed rarely with weak radial threads;
coloration of the recent species rarely disposed in patterns
and usually pale, many species being white. The periostracum
is usually thin and polished.
These rather large and rotund shells are very much
in evidence in the Tertiary and Recent faunas. The
Recent species number about 100 and have an almost
universal distribution in the temperate and warmer
inshore waters.
The genus is relatively scarce in the faunas of the
Alum Bluff group, a single species only having been
recognized at each horizon. The three species are
closely related and all referable to the section
Dosinidia, but the differences which separate them,
though slight, are constant.
Concentric lamellae sharply elevated toward the posterior
margin:
Basal margin obscurely truncate.
Dosinia (Dosinidia) chipolana Dall.
Basal margin evenly rounded.
Dosinia (Dosinidia) liogona Dall.
Concentric lamellae closely appressed toward the posterior mar-
gin_______-___-__-_Dosirua (Dosinidia) dalli Gardner, n. sp.
Section DOSINIDIA Dall
1902. Dosinidia Dall, U. S. Nat. Mus. Proc., vol. 26, p. 347.
Type: Venus concentrica Born. Recent off the east
coast from Hatteras to Aspinwall.
Dall 4 describes this group as follows:
Valves suborbicular, more or less compressed, white, with a
sculpture of concentric grooving, the interspaces never lamel-
lose; furnished with an obvious periostracum; lunule small,
impressed; escutcheon absent; pallial sinus ample, ascending,
angular in front; middle cardinals broad, sulcate or bifid,
anterior lateral small, feeble, smooth.
This group is confined to the tropical and warmer temperate
waters of America, where it replaces all the other sections of
the genus. The nepionic young have the posterior cardinals
corrugated and there are obscure traces of a posterior lateral,
but these characteristics are soon lost and leave no traces in
the adult.
> Dall, W. H., op. cit., vol. 3, pt. 6, p. 1227, 1903.
< Idem, p. 1229.
VENERACEA 153
Dosinia (Dosinidia) chipolana Dall
Plate XXIV, Figure 1
1903. Dosinia (Dosinidia) chipolana Dall, Wagner Free Inst.
Sci. Trans., vol. 3, pt. 6, p. 1229, pi. 54, fig. 4.
Dall describes this species as follows:
Shell rather small and thin, suborbicular, moderately con­
vex, with full, pointed beaks, with fine, sharp concentric
grooves having the distal side more abrupt, the interspaces
flattish and hardly raised toward the ends of the shell; lunule
lanceolate, impressed; beaks sculptured like the rest of the
shell; anterior dorsal margin convexly arched; hinge plate
rather short and wide; teeth normal; the adductor scars large;
the pallial sinus ample, ascending, acute in front, terminating
two-thirds the distance forward from the posterior to the
anterior adductor. Height 36.5, length 39.0, diameter 17.0
millimeters.
The nepionic young of this species have very much the form
of the adult and are usually sculptured in much the same way.
Type: U. S. Nat. Mus. No. 114576.
Type locality: No. 2211, Alum Bluff (lower bed),
Liberty County, Fla.
A few juveniles with the concentric sculpture uni­
formly developed over the entire valve occur in the
marl at Tenmile Creek. They probably represent a
distinct and undescribed species. The Chipola species
is relatively broader than D. liogona from the Oak
Grove or D. dalli from the Shoal River. The charac­
ter of the sculpture and dentition is similar to that of
the former. Dosinia chipolana Dall is common at
Alum Bluff and fairly well represented at other locali­
ties in the marl. The individuals from Sopchoppy
are casts but apparently identical with those from
Chipola River.
Occurrence: Chipola formation, localities 7893r,
2212?, ?7257r, 2213?, 3419r , S715P, 2211 C,7183 C,?7468 C .
Dosinia (Dosinidia) liogona Dall
Plate XXIV, Figure 2
1903. Dosinia (Dosinidia) liogona Dall, Wagner Free Inst. Sci.
Trans., vol. 3, pt. 6, p. 1230, pi. 54, fig. 11 (in part).
Dall describes this species as follows:
Shell much resembling the last, from which it differs by the
less convex posterior dorsal margin; smooth or feebly sculp­
tured beaks, sculpture rising into sharp, fine lamellae toward
the ends of the shell, smaller adductor scars, narrower hinge
plate, and different form of the nepionic young. Height 45,
length 48, diameter 18 millimeters.
The young shells are proportionately more elevated and
shorter than the adult and most of them are smooth or very
sparsely concentrically grooved. At first sight they would
hardly be recognized as the same as the adults. The posterior
cardinals are elegantly crenate. In the adult the anterior
left and posterior right cardinals are grooved on the distal
edge.
Type: U. S. Nat. Mus. No. 135891.
Type locality: No. 2646, Oak Grove, Yellow River,
Okaloosa County, Fla.
The sharp elevation of the concentric lamellae as
well as the less evenly rounded umbonal area serve