.TUKES-BROWiNi; : DOSI.MA AND ITS SUBDIVISIONS. 97 



should be reierred to it, but D. htpatica sliould not, because its liinule 

 is uot impressed, and it has uo escutcheon. One wonders whether he 

 would iuclude such shells as D. ccevulea and B. subrosea, which ap;ree 

 with his wide definition except in regard to their pallial sinus, which 

 is short, broad, and nearly horizontal, not ascending. 



His Orhiculus section he briefly defines as follows: "There is no 

 escutcheon, the pallial sinus is very long and narrow, and the anterior 

 lateral is strong." As a matter of fact the anterior lateral is no 

 stronger in B. exolefa than it is in B. Imcta, while the middle cardinal 

 of the left valve shows differences -which Dr. Dall failed to perceive 

 or to think of any importance. 



I have elsewhere pointed out that under the present rules of 

 zoological nomenclature Da Costa's genus Pedunculus must be 

 recognized, and I selected his P. capillaceus (Bo.sinia exoleta) as the 

 most convenient type. Hence the name Orhiculus must give place to 

 Pectunculus. The B. exoleta group is easy to recognize as a natural 

 section ; it includes B. radiata, Sow. (which is probably only a West 

 African variety of exoleta), B. erythrceci, Homer, B. anipJtidesmoides, 

 Iveeve, B. grata, Desh., B. nohilis, Desh., B. Jiepatica, Lam., and 

 J), sculpta, Hanley, with probably B. conglobata, Romer, though I have 

 not seen a specimen of that species. 



Bosinidia. — This section appears to represent the preceding group 

 on American coasts, but differs from Pectimculus in the bright shining 

 white surface of the shells, the sculpture being of flattened riblets 

 separated by grooves, and in having a short angular pallial sinus. 

 Dr. Dall also notes that in the nepionic young the posterior cardinal 

 teeth are serrate or corrugated, though generally smooth in the adult; 

 in B. Bunheri, however, this condition sometimes persists, and I have 

 a specimen in which it is clearly seen. 



This section includes B. concentrica (Rom), type; B. elcgans, 

 Conrad ; B. discus, Heeve ; B. ponderosa, Gray ; B. distaiis, 8ow, 

 (if distinct from ponderosa) ; B. Bunlierx, Phil. ; B. Amice, Carp. ; 

 B. oiitens, Eeeve; which, however, is probably only a synonym of 

 D. Patagonica, Phil. It must also include B. plana of Chinese waters, 

 which is closely allied to discus, and consequently the section is not 

 restricted to American seas as stated by Dr. Dall. B. plana and 

 B. discus are the two most compressed and flattened species of the 

 genus. B. Hanley ana {= B. simplex, Hanley) also probably belongs 

 to this section, and is found at Singapore and in the Gulf of Siam. 



Austrodositiia. — For this section Dr. Dall chose B. amis as his type, 

 and he defined it as having the "lunule deeply impressed, escutcheon 

 impressed and bordered by prominent keels; pallial sinus short and 

 angular; anterior lateral and the pit into which it is received, and 

 some of the anterior cardinal teeth sharply corrugated; the middle 

 cardinals bifid ". This description, however, is hardly correct, for the 

 escutcheon of B. anus is only well defined in the left valve, the 

 concentric riblets of the right valve being continuous to the ligamental 

 margin. It does not differ, in fact, from the escutcheon of many species 

 belonging to the typical section. Again, the middle cardinal teeth 

 are not bifid in adult shells, being merely rugose; in young shells the 



