18 ME, MACDONALD ON THE ANATOMY 



sisting of an interior grooved, and a posterior glandular portion, — the latter 

 being homologous with the trailing bulb of Firoloides^ and, I believe, also with 

 the trumpet-like segment of Atlanta. 



The rachidian plates of Carcliapoda (Plate I. fig. 11, o ; Plate II. fig. 5, c), are 

 broad and slightly concave in front, but rather more so behind, with the angles 

 obtuse in front, and sharp and incurved posteriorly. The dental processes are 

 only three in number, — the central one being large and broadly conical, and the 

 lateral ones very small. 



The little tooth on the inner side of the principal fang of the first pleural 

 series is distinctly developed, but the uncini do not appear to differ in any essen- 

 tial particular from those of Firola. 



Carinaria Gaudichaudi (Plate II. Figure 4.) 



This species I found to have as wide a range as the Firoht and Firoloides 

 previously described. Its length varies fi-om 1^ to 2 inches, and altogether it 

 looks like an Atlanta whose head and body had much outgrown the capacity of 

 its shell. On comparing the shells of the two genera, the}-^ will be found to 

 resemble one another in several particulars. Thus, they are both dextrally- 

 spiral, with a distinct umbilicus in the axis of the spire, and a prominent keel 

 on the dorsal border of the whorls ; but both shell and keel in CarinaHa are 

 beautifully crimped transversely, and the last whorl increases very rapidly in 

 keeping with the development of the animal, so that the mouth of the full grown 

 shell is widely separated from its spiral nucleus. 



The body is pellucid and colourless, but slightly, or not at all, tuberculated. 

 The inner surface of the integument, however, is studded at pretty equal dis- 

 tances with little clusters of cells like those of Firoloides. M. Rang believed 

 that a tuberculated epidermis was always present in Carinaria, fonning a distin- 

 guishing feature between it and Firola, in which, according to him, the outer 

 integument is always smooth (?) He makes allusion evidently to the little 

 clusters of cells above noticed as the representatives in Firola of the tubercu- 

 lations of Carinaria. 



The proboscis is abruptly truncated at its extremity, and very variable as to 

 its length and fulness. The eyes are fronted by small tentacula, and the acoustic 

 sacs, as in Cardiapoda, ho.., are appended to long and delicate auditory nerves. 

 The ciliated lining of the sacs in this species I have been enabled to observe more 

 distinctly than in any of the other Heteropods described above. 



The abdominal fin is fan-shaped, with a thin transparent margin ; and the 

 sucker-disc is represented by a little cup-like dilamination of its posterior border. 

 The tail, or metapodium, is laterally compressed, and tapers to a point, without 

 supporting an obvious rudder-fin, like that commonly given in figures of Carin- 

 aria mediterranea. 



