MUSEUM OF COMPARATIVE ZOOLOGY. 269 



Se<juenz'ux formosa and var. uitida Verrill, Conn. Acad. Trans., VI. p. 18G, pi. xxxi. 



figs. 14, 14 a, 14 b, May, 1HH4. 

 1 Seguenzia eritiina Verrill, loc. cil., VI. p. 189, pi. xxxi. fig. 15. 



Habitat. Station IG, 292 fms.; Station 20, 220 fnis.; Barbados, 100 fms. 

 Off the Florida coast, in 205 fni.s., Dr. linsh. 



In cxaniinin«^ the specimens of Seguenzia in the Jeffreys collection, including 

 types of Se<^uenza's " Trochocochlea monocingulata" as well as specimens ob- 

 tained by the Blake and the U. S. Fish Commission at various points, I find 

 myself in a dilemma. Either each separate individual is to be regarded as a 

 species, or the variability of the shells is very great. Persistent study of the 

 specimens has convinced me that the latter is the true solution, and that the 

 most evident characters, such as the umbilicus (in some adult s])ecimens) may 

 be present or absent; that the number of spiral threads, their strength and 

 sharpness on the basal disk, are entirely inconstant, and, while in the typical 

 formosa the ridge next to the suture is waved or granulate, in many it is per- 

 fectly plain. 



It is for this reason, and having several specimens apparently intermediate 

 between the type and the form named eritima by Prof. A^errill, that I have 

 been led to suggest their identity, though I have not seen Prof. Verrill's types. 

 In any case, his name would hold for a well marked variety. 



Family TRICHOTROPID.^. 



Genus TRICHOTROPIS Sowerby. 



None of the typical forms of the genus are found in the tropics. The de- 

 gree of affinity which Mesostoma, Dolophanes, etc. bear to the original type of 

 the family yet remains to be determined. 



Subgenus MESOSTOMA Deshates. 



Mesostona Desh., An. s. Vert. Bas. Paris, II. p. 416 ; 1st sp. M. pulchra Desh., loc. 

 cit., pi. xxviii. figs. 13-16, 1864. Eocene, Paris Basin. 



^ Cerithioderma Conrad, Journ. Acad. Nat. Sci. Phila., 2d ser., IV. p. 205; sole ex- 

 ample, C. prima Con., loc. ciL, p. 295, pi. xlvii. fig. 30, Feb., 1860. Eocene, 

 Alabama. 



It is impossible to say from Conrad's figure whether his Cerithioderma is 

 identical with Mesostoma Deshayes, or not. There is nothing to separate the 

 two shells as far as the figures go, but Conrad in his diagnosis says of the canal, 

 " beak very short, narrow, recurved." The last epithet will in no wise apply 

 to our shell, nor to Deshayes's Mesostoma. I suspect it to be an error, notwith- 

 standing which I prefer not to adopt Conrad's name, which has priority, with- 

 out inspecting his type if it be accessible. 



