STJBEMARGINULA. 273 



*** 



RIMULA ECHINATA Old. Gaspe Straits. 



" An imperfect description from the figure of a shell unfortunately 

 lost or missing. * * * may possibly be jR. propinqua A. Ad." 

 (Gld. Proc. Bost. Soc. vii, p. 163). 



Genus SUBEMARGINULA Blainville, 1825. 



Subemarginula BLAINV., Manuel de Malacol. p. 501, type Em. 

 emarginata Blainv. Hemitoma SWAINSON, Malacol. p. 356. Siph- 

 onella ISSEL, Mai. Mar Rosso, p. 232, 1869. 



Shell rounded-oval, conical, apex near the middle, curved back- 

 ward ; surface radiately ribbed ; anal notch generally short, contin- 

 ued upward as a groove inside, occupying the end of a slightly 

 prominent anterior rib, which is not sculptured differently from the 

 other ribs. 



The great muscle scar exhibits a peculiarity diagnostic of this 

 genus : its anterior terminations are recurved and produced inward 

 toward the cavity of the apex. This character is found in all of 

 the sections I have grouped under Subemarginula, including Tugalia. 



This genus differs from Emarginula in having no distinctly dif- 

 ferentiated anal fasciole extending upward from the notch or slit in 

 the front edge of the shell. This slit is usually a little to the right 

 of the middle. 



Several sections may be distinguished : 



SUBEMARGINULA s. s. Shell short-oval, apex near the middle, 

 a groove continuing upward inside from the anal notch. 



Under this as subsections may be grouped (1) Clypidina Gray, in 

 which the anal notch is short, the space within the muscle-scar hav- 

 ing a dark mushroom-shaped figure; this includes most of the ori- 

 ental species. (2) Plagiorhytis Fischer, like the last, but the anal 

 notch distinctly to the right, includes S. stellata and S. sulcifera. 



TUGALIA Gray. Shell oblong, depressed, apex posterior, front 

 margin without a notch, either rounded or sinuous ; no internal 

 anal groove ; no enlarged rib in front. 



Section SUBEMARGINULA s. str. 



American species. 

 S. OCTORADIATA (Gmelin) Ad. PL 29, figs. 17, 18, 37. 



Primary ribs 8, not forking or double ; front margin scarcely 

 notched. 

 18 



