246 Mr. E. Billings on the Genus Athyris. 



clara and A. Maia) which, no doubt, belong to the genus. The 

 others with perforated beaks I marked doubtful, thus : — A. (?) 

 scitula (Hall) ; A. (?) Clusia, n. sp. ; A. (?) unisulcata (Conrad) ; 

 A. (?) rostrata (Hall) ; A. (?) Chloe, n. sp* 



" I think it the same as the species called Meristella Boris by 

 Prof. Hall (13th Reg. Rep. p. 84, 1860). I doubt that any of the 

 others belong to either Athyris or Spirigera." 



Afterwards Prof. Hall (13th Reg. Rep. p. 74) proposed to es- 

 tablish a new genus, Meristella, precisely identical with Athyris 

 as redefined by M'Coy in 1852. His diagnosis reads thus : — 



"Shells variable in form, oval, ovoid, orbicular, or transverse. 

 Valves unequally convex, with or without a median fold and sinus ; 

 beak of the ventral valve apparently imperforate, incurved over the 

 beak of the smaller valve ; area none ; valves articulating by teeth 

 and sockets. Surface smooth, or with fine concentric lines of growth 

 and fine obsolete radiating striae, which are usually more conspicuous 

 in the exfoliated shell. The interior of the dorsal valve is marked 

 by the presence of the longitudinal septum, and the upper part of 

 the ventral valve by a deep subtriangular muscular impression which 

 unites with the rostral cavity." 



Now I hold that, instead of proposing a new genus, he should 

 have retained the original name Athyris, because his proposition 

 amounts to a subdivision of the group : and, according to the 

 laws of nomenclature, he should have applied the old name to 

 that portion for which it is most appropriate, as had been done 

 six years before by Davidson. As soon as this new arrangement 

 was published, I reinvestigated the subject, and perceiving that 

 it amounted to nothing more than a restoration of Davidson's 

 former classification, but with a change of names, I declined to 

 adopt it. In all the publications of our Survey in which species 

 of this group are described or figured, Athyris is used instead of 

 Meiistella. 



On the merits of this classification, a note in ' Silliman's 



* I now think that A. clara is the same as Prof. Hall's Meristella nasuta, 

 but am not quite sure that it is Conrad's species. A. [1) scitula was after- 

 wards found to belong to a new geuus described by me under the name of 

 Charionella {op. cit. vol. vi. p. 148, March 1861). It is not Atrypa scitula. 

 Hall, a point on which I was not certain at the time, as will be seen by 

 the description, which reads thus : — 



" The above figures represent diiferent views of two specimens of a spe- 

 cies which appears to me to be identical with that figured in the work 

 above cited. It varies greatly in size. The length of the largest specimen 

 that I have seen is 17 lines, the greatest width 14 lines, depth 8 lines. The 

 smallest is about 2 lines in length ; and many of intermediate sizes have 

 been observed, to make out the series. It is not certain that this species 

 belongs to the genus Athyris." — Op. cit. p. 30. 



