Terrestrial Opcrculate Mollusca from TVinidad. 245 



are the two tentacles with the eyes close behind them. The 

 foot is produced in front into two acute lobes. 



It may seem strange that so much variation should exist in a 

 single species — from a shell with smooth whorls to one with 

 whorls bearing a keel ornamented with aculeate projections ; but 

 there does not exist in my mind the smallest doubt of the dif- 

 ferent forms belonging to the same species. All the forms are 

 found existing together in the streams of northern Trinidad. 



Valvata agglutinans, n. sp. 



Shell trochiform-deprcssed, perforate, entirely composed of nu- 

 merous minute grains of mineral matter ; whorls 3-4, almost 

 cariuate, flattened beneath ; umbilicus circular ; aperture very 

 oblique, circular, the margins shortly united on the penulti- 

 mate whorl ; peristome simple, irregular. Height 01 inch, 

 greatest breadth 0*17 inch. 



This very curious little Valvata makes its shell almost entirely 

 of minute particles of quartz and mica, the cementing material 

 being very limited in amount. It lives on the surface of rocks 

 and stones in the hill-streams of the northern part of Trinidad. 



§ 2. Terrestrial Species. 

 Cyclotus trinitensis, n. sp. 



Shell depressed, turbinate, rather thick, white under a pale- 

 brown epidermis, with fine wavy lines of growth, and some- 

 times with obsolete white or chestnut bands; spire somewhat 

 acuminate ; whorls 5, convex ; umbilicus broad and open j 

 aperture slightly oblique, nearly circular ; peristome blunt, 

 its margins forming an angle above ; right margin slightly 

 sinuate. Operculum concave, with six obUquely striate 

 whorls, the inner margins of which are raised. Height 0'55 

 inch, greatest breadth 0*9 inch. 



The animal is of a pinkish colour, which is most pronounced 

 about the tentacles. The eyes are small and black. The mouth 

 is provided with an amber-coloured, somewhat triangular man- 

 dible, divided into two parts by a median fissure, from which 

 diverge slightly cur^'cd rows of minute denticulations strongly 

 resembling the lingual teeth of some Helicidse. 



The lingual teeth are 3 . 1 . 3, in arched rows : central broad, 

 tridentate; 1st lateral broad, bidentate, with a base much pro- 

 duced outwardly; 2nd tridentate; 3rd much hooked and re- 

 flexed, tridentate. This dentition is very like that of Cijclophorus 

 Tuba (Gray, Syst. Dist. Moll. p. 78). 



This species is readily distinguished from C. jamaicensis by 

 its light colour and by the absence of any ridge round the um- 



