PTEROPODA, 105 



talline ; oblong, pointed at the vertex, truncated at the base; 

 general shape like a Turkish slipper. Two inches long. Inha- 

 bits the Mediterranean. 



Genus 2.— LIMACINA Lamarck. 



Generic Character. — Body soft, oblong, two branchial fins 

 situated at the base of the neck ; posterior part of the body spi- 

 ral, and enveloped in a shell — Shell thin, fragile, papyraceous, 

 spiral, with the volutions articulated in a discoid form. 



Limacina helicialis — The Helix-like Limacina. Plate 

 XIV. fig. 11. Thin, fragile, spiral ; the volutions united in a 

 discoid form. Half an inch in diameter. Inhabits the North 

 seas. 



Genus 3.— CLEODORA.— Peron. 



Generic Character. — Body oblong, gelatinous, contractile •, a 

 head 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 tentacula ; two 

 opposite membranaceous, pellucid, and cordated wings, placed 

 at the base of the neck. — Shell gelatinoso-cartilaginous, trans- 

 parent, and in the form of a reversed pyramid. 



Cleodora pyramidata. — The Pyramidal Cleodora. Plate 

 XIV. fig. 9. Pyramidal, triangular; of a gelatinous or carti- 

 laginous substance, very thin and transparent; aperture obliquely 

 truncated. Inhabits the American seas. 



Genus 4.— HYAL^A. — Lamarck. 



Generic Character. — Body enclosed in a shell, winged before ; 

 two opposite wings, somewhat retractile, inserted at the sides of 

 the mouth ; head indistinct; mouth terminal, placed at the junc- 

 tion of the fins ; without eyes ; branchiae lateral ; shell horny, 

 transparent, oval-globular, with three teeth behind, open at the 

 summit and the two posterior sides, 



HyalcEa tridentata. — The Three- Toothed HyaLxEa. Plate 

 XIV. fig. 12. Transparent, horn-coloured, globular ; posteriorly 

 tridentate ; summit and two posterior sides open ; very finely 



