474 Dr. P. P. Carpenter on new Forms of Mollusks 



ledge of the habits of these insects is still in its infancy. The 

 few facts we know are perhaps crude and imperfect ; and it is 

 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 Philip P. Carpenteh, 

 B.A., Ph.D. 



[Continued from p. 316.] 



15. Nacella peltoides. 



N. testa parva, Isevi, cornea, subdiaphana, ancyliformi, apice elerato, 

 valde insequilaterali, strigis pallida castaneis radiata ; intus niti- 

 dissima, subaurantia. Long. '14, lat. 'll, alt. *05 poll. 



= Nacella, sp. ind., Maz. Cat. no. 262, p. 202. 



16. Acmaa (?var.) atrata. 



A. testa solida, rugosa, conica, apice paulum antrorsum sito ; extus 

 costis crebris rotundatis irregularibus, hie et illic majoribus 

 sculpta, baud apieem versus discordanter corrugatis ; interstitiis 

 minimis ; intus alba, castaneo et nigro varie maculata ; margine 

 latiore, nigro tessellato. Long. 1*3, lat. TO, 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. Acmaa strigatella. 



A. testa A. mesoleucce simili, sed minore, baud viridi ; striolis mini- 

 mis, confer tissimis, 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 beheved 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 1 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), I do 

 not wish to encumber the valuable pages of the ' Annals ' by a discussion 

 of them.— P. P. C. 



