CONCHOLOGY. 81 



1. Genus Hyalaea. 



Animal. Body enclosed in a shell, winged before, two opposite 

 wings, somewhat retractile, inserted at the sides of the mouth, 

 head distinct, mouth terminal, placed at the junction of the fins 

 without eyes. 



Shell. Symmetrical, very thin and transparent, valves unequal, 

 flat above, convex below, open like a cleft anteriorly, summit 

 truncated and tridentated posteriorly. Inhabits the Mediterranean. 

 Two species. 



Hyalsea tridentata. Hyalsea cuspidata. 



2. Genus Clio. 



Animal. Body free, naked, more or less elongated, tapering to 

 the rear, head very distinct; provided with six long conical 

 retractile tentaculse, separated into two groups of three each ; mouth 

 altogether terminal and vertical, eyes sessile, rudiment of a foot 

 under the neck. 



This is a molluscous animal without any testaceous covering, 

 but is here placed as leading to other genera which have shells. 

 Inhabits the Indian seas. Two species. 



Clio borealis. Clio Australis. 



3. Genus Cleodora. 



Animal. Body oblong, gelatinous, contractile; ahead in front 

 with two wings, and the posterior part enveloped in a shell, head 

 distinct, projecting and round ; two eyes ; mouth in the form of a 

 small beak ; destitute of tentaculae; two opposite membranaceous 

 pellucid, and cordatcd wings, placed at the base of the neck. 



Shell. Pyramidal, triangular, of a gelatinous or cartilaginous 

 substance, very thin and transparent ; aperture obliquely trun- 

 cated. Inhabits the South American seas. Two species. 

 Cleodora pyramidata. Cleodora caudata. 



4. Genus Limacina. 

 Animal. Body soft, oblong, two branchial fins situated at the 

 base of the neck ; posterior part of the body spiral, and enveloped 

 in a shell. 



