MUSEUM OF COMPARATIVE ZOOLOGY. 41 



little consequence, the main point being the identification of Sowerby's 

 shell with the specimens before me, which may be regarded as certain. 

 The habitat of the species is undoubtedly African, the localities " Rio," 

 " Bodegas," etc., being erroneous. 



The fact of the type being settled, only one course remains, — to rear- 

 range the genus in accordance with the facts. Objections may, and probably 

 will, be raised against such rectifications, but accuracy being the aim and 

 basis of all science, nothing else is worth regarding, and rectifications, 

 however long delayed, are inevitable at last. 



The species has been well described by various authors, and there is 

 nothing further in regard to it for me to add. The catalogue number of 

 Dr. Gould's types, in the Smithsonian Cabinet, is 5962. They were ob- 

 tained at Cape Palmas, West Africa. The exceedingly minute foramen 

 hidden beneath the septum might well excuse Dr. Gould for calling it a 

 Crania. I am not aware of any other species of true. Discina in a recent 

 state, but there are several species usually denominated Discina, with 

 which I am unacquainted autoptical])'. 



There are no species of Orbiculoidea or Trematis known in a recent 

 state. 



The following species of Discinisca have been found living. I have ex- 

 amined only those after which an exclamation-point is placed. 



Discinisca stella! Gould, Proc. Bost. Soc. Nat. Hist., VII, p. 323, Sept., 1860. 



— Reeve, Conch. Icon., pi. 1, fig. 1, 1862. 

 Singapore and Phillipines. Cumixg. China Seas. Stimpson. 



Discinisca lamcllosa ! Broderip, P. Z. S., 1833, p. 124. — Reeve, Conch. Icon , 



pi. 1, fig. 3, 1862. 

 Panama to Peru. 



Type of the subgenus. I have examined an immense number of speci- 

 mens from Panama, and find that they exhibit many varieties. The apex 

 of very young shells is circular, whitish, and of a different texture from 

 the remainder of the shell. This circumstance was first pointed out by 

 Mr. E. S. Morse. The nucleus is probably the remains of the embryonic 

 shell. The species has no radiating stria?, and is a thinner shell than 

 l&vis. 



Discinisca tenuis Sby., Thcs., I, p. 366, pi. 73, figs. 4, 5. (not Reeve, Conch. 



Icon., pi. i, fig. 5, 1862). 

 Hah.? 



Reeve's figures of " Orbiculis tenuis " do not represent Sowerby's species, 

 but agree very well with some of the varieties of D. lamellosa. I have seen 

 no specimens of either of the former species, but the figures exhibit dis- 

 crepancies too great to be reconciled. Sowerby gives no localities, and 



