known as Gemma, Parastarte, and Psephidia. 479 



it lias the same method of protecting its young. Until it baa 

 been proved that the animals are different, it seems to me 

 more convenient to group them together in one genus. 



4. Acolus, J-13r., 1913. 



In 1910 Messrs. Cooper and Preston, describing some 

 "New Species of Shells from the Falkland Islands"* 

 referred one of them to "Psephis" under the name of 

 P. foveolata. By the kindness of Mr. J. E. Cooper I have 

 been able to examine good specimens of this species, and find 

 that it differs in several important respects from Psephidia 

 (i. e., Psephis). The dentition of the left valve is similar, 

 except that the posterior tooth is shorter and more oblique ; 

 but in the right valve there are only two teeth, equally 

 divergent from the umbo, and evidently representing the 

 normal posterior and median, so that the anterior is obsolete. 

 There is only a slight inflection of the pallial line, not a real 

 sinus, and the valve-margins are smooth, showing no trace of 

 crenulation or striation except on the dorsal slopes. 



These dorsal slopes have peculiar features : the left ante- 

 rior and the right posterior margins are grooved as usual, but 

 more narrowly than in Psephidia ; the left posterior margin 

 is raised into a low ridge, which is longitudinally but irregu- 

 larly striated, and the opposing margin of the right valve is 

 not only grooved, but correspondingly striated inside the 

 groove. These fine striations can only be properly seen 

 under a 1-inch objective. 



From the above description it will be seen that the shell 

 referred to Psephidia by Messrs. Cooper and Preston differs 

 from the type of that genus in the following particulars : — 

 (1) in the smooth ventral margins; (2) in the peculiar 

 striation of the posterior dorsal margins ; (3) in the absence 

 of a left anterior tooth ; (4) in the absence of a pallial sinus. 

 These differences are, in fact, greater than those between 

 Gemma and Parastarte, and are quite too great to allow of 

 the shell being regarded as merely a species of Psephidia. 

 It must therefore rank as a subgenus, and as it will require a 

 new name, I now propose that of Aeolus, from ukoXu^, a 

 crumb or morsel. 



Since, however, I have already proposed to place Psephidia 

 as a subgenus of Gomphina, and since Aeolus can equally 

 well be brought under the same generic definition, 1 will 

 conclude by giving a formal definition of the genus Gomphina 

 and the subgenera which may be attached to it. 



* Ann. & Mag. Nat. Hist roL v. p. 110 (1910). 



