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634 R. C. PUNNETT.No. of Specimen.(1) (2) (3) (4) (5) (6) (7) (8)Length of collar 3 3 3 2-5 2-5 25 1-5 ——„ „ proboscis 5'5 6 5 5 4'5 4'5 4„ „ branchial region ... 20 17 16 17 17-5 17 10-5 9Total length _ 215 — — — — — —Branchial length^.^ ^.^ ^.3 ^.^ ^ 6-8 7-Collar lengthNo. of gill slits 116 — 110 104 102 88 74 58The specimens are given in order of size, (1) being the largest, (8) the smallest.In his account Willey states that external liver saccules are not present in the alliedspecies S. alba ('99, p. 277), "although, when fresh, the annular ridges were found to beturgid and to present the appearance of rudimentary saccules, an appearance which wasalmost entirely lost after preservation." He was unable to state anything with regard tothis region in Sp. porosa as his only well-preserved specimen lacked the post-genital portionof the body. External liver saccules are nevertheless present in Sp. porosa, though they arenot very prominent (PI. XXXIX. fig. 13). That they project somewhat from the dorsalsurface may be more readily seen in transverse sections (see PI. XLI. fig. 5). They arealso characterized by their green colour.Pig. 120. Schematic reconstruction of anterior end of Sj). porosa, x 10. The dotted line in front of the stomoohordindicates the forward extension of the pericardial auricles. For lettering see p. 676.Internal structure. To the full and careful account given by Willey I have littleto add, and that chiefly in regard to the jjost-genital region which, as has already beenmentioned, was absent in his specimen.Proboscis. In Willey's specimen the ventral recurrent vessel was independent of theventral septum. In the three si^ecimens which I have examined it runs up to the centralcomplex in the anterior free edge of the ventral septum (Text-fig. 120, vrv.).Willey states that the median muscular system extends over about ^ of the lengthof the proboscis. It is not quite so long in the Maldive forms and may be exceedinglyshort (Text-fig. 120, mdv.), not extending quite so far forwards as the pericardial auricles.