42 



Order 7. NUCLEOBRANCHIATA. 



Branchiae; plumose, forming, in connection with the visceral or- 

 gans, an external nucleus, capped ivith a delicate glassy shell. 



The gelatinous swimmer, represented in Plate K, appears to have little 

 of the character typical of the class Gasteropoda, but the natatory fin of 

 Carinaria is supposed to be the equivalent or homologue of the Snail's 

 locomotive disc. The branchiae form part of a nucleus which, it may be 

 observed, is quite external to the body, and they communicate with the 

 head and mouth by means of a long connecting gut. 



Carinaria. 



Genus 1. CARINARIA, Laniard: 



Animal ; body gelatinous, swollen, prickly, a little compressed at 

 the sides, attenuately acuminated posteriorly ; head prolonged 

 into a trunk armed icith symmetrical horny processes ; tentacles 

 two, having at the base of each a conspicuous eye ; visceral 

 mass and branchiae contained in an outer nucleus communicating 

 by a gut with the mouth ; covered by a transparent glassy shell ; 

 below the body is a vertical fin. 



Shell ; cap-shaped, very thin, hyaline, corrugate, attenuated into 

 a hooked vertex, furnished along the back with a keel, which is 

 either simple or toothed. 



The f Glassy Nautilus/ as the delicate transparent shell of Carinaria has 

 been long erroneously called, is, perhaps, the most remarkable production 

 in the whole conchological series. The Carinaria is a swollen transparent 

 mass of gelatine, having a well-developed head, with tentacles and eyes 

 and a powerfully-armed proboscis for the seizure and elimination of food ; 

 but the viscera and branchiae are gathered into a nucleus outside the upper 

 dorsal part of the body, communicating with the proboscis by a long at- 

 tenuated kind of gut ; and attached to this nucleus, like a cap, is the well- 

 known delicate little glassy shell. Beneath the gelatinous body is a ver- 

 tical natatory fin, and the animals congregate and swim about rapidly at 

 night, with Firola and other shell-less mollusks of similar character, rest- 

 ing occasionally by the aid of a sucker, which may be observed on the 

 hinder part of the fin.* 



* " The Carinaria tribe," writes Dr. Johnston, in his own delightful style, " need occasional 

 repose and cessation from activity — and how admirably is the foreseen want provided against ! 



