GASTEROPODA. 99 



than the body. Shell thin, obliquely conical; aperture oval, 

 with a pointed apex, which is inclined backwards ; margins 

 simple. 



Ancylus oblongus. —The Oblong Ancylus. Plate XIV. 

 fig. 18. Aperture elongated, vertex turned to one side ; with 

 fine concentric striae ; pale horn-colour above, inside bluish. 

 One-third of an inch long. Inhabits the fresh waters of Eu- 

 rope. 



Genus 15.— CREPIDULA.— Zawjcrcy^. 



Generic Character. — Head of the animal anteriorly forked, 

 having two conical tentacula, with the eyes placed at their ex- 

 terior base J mouth simple, destitute of jaws, and situated in 

 the bifurcation of the head ; branchicB with tufts and projecting 

 from the branchial cavity ; the mantle never bordering the shellj 

 foot minute : anal orifice lateral ; shell ovate^ or oblong-ovate, 

 convex on the back, and concave beneath ; spire inclining to 

 one side ; aperture with a horizontal partition next the spire, 

 extending to nearly the middle of the shell. 



Crepidula aculeata. — The Prickly Crepidula. Plate 

 XIV. fig. 16. Oval, brown, with acute rough striae ; vertex re- 

 curved ; inside with a chamber, and bluish or purple. One inch 

 long. Inhabits the American seas. 



Genus 16.— CALYFTRMA.— Lamarck. 



Generic Character. — Animal unknown. — Shell conical, base 

 orbicular, and summit vertical, imperforate and acute ; internal 

 cavity with a spiral septum. 



Calyptrcea Sinensis. — The Chinese Calyptr^a. Plate 

 XIV. fig. 19. Orbicular, subconic •, vertex ending in a small 

 volution ; smooth, margin entire ; cream-yellow ; very glossy 

 within, and provided with a laminar plate. Three-fourths of an 

 inch in diameter. Inhabits the Chinese seas. 



Genus 17.— PILEOF SIS.— Lamarck. 



Generic Character, — Animal with two conical tentacula, and 

 the eyes at their base ; branchicB formed in a row under the an- 

 i2 



