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. (?) Chloé, n. sp.* 
“T think it the same as the species called Meristella Doris 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 striee, 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 
Meristella. 
On the merits of this classification, a note in ‘ Silliman’s 
* T 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. (?) scitula was after- 
wards found to belong to a new genus 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 different 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. 
