TROCHUS. 315 



the mantle. The fry of T. umbilicatus is white, nearly 

 flat, and has only two or three prominent ribs. 



It is the T. obliquatus of Gmelin, T. umbilicaris of 

 Pennant, T. cinerarius of Pulteney and Lamarck 

 (though neither of the two latter are Linnets species so 

 named), and Gibbula lineata of Leach. 



C. Very small, circular, nearly flat-spired, with an exceedingly 

 wide and open umbilicus. Oirculus. 



N! 320 8. T. DUMI'NYI *, Requien. \{ 



Delphimda Duminyi, Eeq. Cat. Cors. p. 64. 

 Animal not known. 



SHELL orbicular, rather solid, but semitransparent and 

 somewhat glossy: sculpture, 8-10 sharp and narrow spiral 

 ridges on the upper part of the last whorl, half that number 

 on the penultimate whorl, and two or three on the next, the 

 upper two whorls being smooth ; the lowest ridge is placed just 

 under the periphery, and is usually stronger and more pro- 

 minent than any of the rest (from which it is frequently 

 separated), and it encloses the umbilical area ; sometimes 

 this part is also ridged ; the furrow between each ridge is 

 crossed by curved microscopical striaB : colour white : spire 

 scarcely raised, but the apex is well defined : whorls 5, cylin- 

 drical and gradually enlarging : suture distinct, although not 

 deep : mouth squarish, obliquely truncated as in other species 

 of Trochus belonging to the last section : outer lip flexuous, 

 with a sharp edge, strengthened a short distance within by 

 a slight rib : inner lip somewhat thickened and reflected 

 towards the umbilicus, and adhering to a considerable part of 

 the periphery of the penultimate whorl : inside porcellanous 

 and polished (not nacreous), exhibiting the outside ridges as 

 dark lines : umbilicus extending more or less over the base of 

 the shell ; it shows nearly as much of the internal spire as is 

 seen of the spire outside ; in some specimens the inner whorls 

 are concentrically striated : operculum circular, with about a 

 dozen volutions, which wind spirally and gradually, and con- 

 verge to the centre. L. 0-035. B. 0-1. 



It 

 * Named in honour of Professor Duminy of Ajaeci 



P 



" . 



