Mr. J. D. Macdonald on the Affiiiities uf the Gasteropoda. 403 



indeed the whole organ, including its armature, very much resembles 

 the dental cheek-pouches of some Pteropods. 



The lingual ribbon of Pletirotoma is exceedingly minute, and the 

 parietes of the sac are not of that dense and unyielding character 

 which they exhibit in Conus, Conorbis*, and Terebra. Moreover, 

 in Pleui-otoma the little lingual membrane is supported by two 

 rounded masses of cartilage composed of large spheroidal cells. The 

 rachis appears to be absent altogether, and there is but a single row 

 of elongated, slightly curved, and sharp-pointed teeth (differing con- 

 siderably from those of Conus and Terebra) in the pleurae. 



The tongue-strap of Mitra^ although remarkably short, is triserial 

 Hke that of Murex, Purpura, &c. ; but the author has invariably 

 found that in those MitrcB in which the sculpturing of the shell was 

 transverse, the pleural teeth were simple, uncinate, and mobile, while 

 in those species characterized by a smooth surface or longitudinal 

 sculpturing, the dental processes were small, straight, and numerous, 

 arising just within the posterior border of broad basal plates. This 

 difference is exactly such as exists between the lingual dentition of 

 the respective groups to which Murex and Tritonidea belong. 



Harpa and Oliua are very closely allied, by the general configu- 

 ration of the body and the characters of the lingual dentition, though 

 it must be remembered that the tongue-strap in the former is so very 

 minute, compared with the whole bulk of the animal, as to appear 

 quite rudimentary. The simple lateral uncini, moreover, are only 

 distinctly visible towards the posterior extremity of the sac. Both 

 these genera seem to be more intimately related to Murex and its 

 congeners than to the Buecinidce. 



Triphoris is now, as it would appear from the characters of its 

 shell alone, placed with Cerithium, but the comparison of the internal 

 anatomy of those genera offers no countenance to their supposed 

 affinity ; thus, single spherical otolithes occupy the auditory sacs 

 of Triphoris, while those of Cerithium contain otoconia. The pro- 

 boscis of the former is long and retractile. The lingual membrane of 

 Triphoris besides, though long and ribbon-like, supports a multiserial 

 pavement of minute teeth, while that of Cerithium is septiserial, resem- 

 bling in many particulars the tongue-strap of Pupina and allied forms. 



The Columbellce deserve to be elevated to the rank of a family, 

 distinguished from the BuccinidcB by the unarmed rachis, and curved 

 versatile pleural teeth of the tongue-strap. 



Although not fully satisfied of the propriety of separating the 

 genus Conidea from ColumbeUa, the author thinks there can be 

 no doubt that Pusiostoma, formerly placed with the ColumbellcB, 

 forms a very distinct genus clearly referable to the BuccinidcB. 



As great difference of opinion has always existed as to the distri- 

 bution of the sexes amongst Gasteropods, so far the author is unable 

 to vouch for the whole truth of the arrangement above given, but he 

 thinks that if there is anything incongruous in it, the correction of 



* Several specimens of a recent species of this genus (hithei-to known only in a 

 fossil state) were obtained from depths ranging between 10 and 20 fathoms, 

 within the barrier reefs surrounding the Feejee Islands. 



2G* 



