474 Dr. P. P. Carpenter on new Forms of Mollusks 
ledge of the habits of these insects is still im its infancy. The 
few facts we know are perhaps crude and imperfect; and itis 
much to be desired that many of the members of this society, ; 
who are so well qualified for the task, would turn their serious 
attention to a branch of natural history where so much that is 
new and interesting remains to be carefully learned and inves- 
tigated. 
: 
; 
XLIV.—Diagnoses of new Forms* of Mollusks collected at Cape 
St. Lucas by Mr. J. Xantus. By Puinie P. Carpenter, — 
BA. PhD. { 
[Continued from p. 315. ] | 
15. Nacella peltoides. 
N. testa parva, levi, cornea, subdiaphana, ancyliformi, apice eleyato, 
valde ineequilaterali, strigis pallide castaneis radiata ; intus niti- 
dissima, subaurantia. Long. ‘14, lat. -11, alt. :05 poll. j 
: = Nacella, sp. ind., Maz. Cat. no. 262, p. 202. ; 
16. Acmea (? var.) atrata. 
A, testa solida, rugosa, conica, apice paulum antrorsum sito; extus 
costis crebris rotundatis irregularibus, hic et illic majoribus 
sculpta, haud apicem versus discordanter corrugatis; interstitiis 
‘ minimis; intus alba, castaneo et nigro varie maculata; margine 
latiore, nigro tessellato. Long. 1°3, lat. 1:0, alt. °5 poll. 
Variat margine nigro-punctato, punctis plerumque bifidis. Variat 
quoque costis parvis, creberrimis ; margine nigro. 
Intermediate between “ P. discors,”? Phil., and “ P. floccata,” 
Reeve. 
17. Acmea strigatella. 
A. testa A. mesoleuce simili, sed minore, haud viridi; striolis mini- — 
mis, confertissimis, plerumque erosis tenuissime sculpta ; albida, 
* As this expression appears to have been misunderstood, I beg to state 
the reason for its adoption. It is no longer believed on all hands that 
every object in nature belongs to some genus or species sharply defined. 
As a working naturalist, I find many intermediate forms which are constant 
in certain characters, and which (for the sake of reference) it is desirable 
to name. I do not choose to profess certainty where I do not feel it, and 
have therefore adopted the formula “ A. (? b. var.) c’”’—thus leaving it to 
the judgment of others, or to the certainty obtained by further research, 
to decide whether c be a variety of 6 or a distinct species. I have found 
* detail’? (not necessarily “‘ portentous”’) far more useful than those loose 
descriptions which may include many widely dissimilar forms, my rule 
always being so to describe that I may recognize the shell at a future time 
without access to the original specimen. Though I cannot acknowledge 
the accuracy of some of the statements in Mr. Reeve’s letter (p. 440), Ido 
not wish to encumber the valuable pages of the ‘ Annals’ by a discussion 
of them.—P. P. C, a 
