155 MARSHALL : ON SOME NEW BRITISH SHELLS. 



Sutton-on-the-Sea, fifteen miles from Skegness — a very gratify- 

 ing discovery, not only as simplifying the drawing and detailed 

 description, but as tending to emphasize the evidence of its 

 British origin. He at once sent it to me, and the following 

 description is taken from this second and perfect specimen : — 



Shell, upper valve ovately triangular, lower valve squarish, 

 both rather convex in the middle ; it is solid for its size, semi- 

 transparent, and slightly lustrous ; sculpture, longitudinal fine 

 and rounded ribs, which are eleven in number on the upper 

 valve and twelve on the lower, they radiate from the beak to 

 the margin, and are separated by interstices nearly equally as 

 broad, they are surmounted with tubercles, varying from six 

 on the side to eight or nine on the centre ribs, and disappear 

 towards the beak, the tubercles becoming more raised and 

 pointed towards the margins ; when examined with a Codding- 

 ton lens the whole of the surface appears crowded with micro- 

 scopical points, being the termination of the tubular perforations 

 characteristic of the genus ; colour glassy white ; margins 

 rounded and scalloped by the ribs, slightly flexuous in front ; 

 beak and auricles very prominent, the latter rather pointed ; 

 foramen or byssal passage large, nearly round ; deltidium (or 

 triangular space below the beak) broad and concave. Length 

 o'o6 ; breadth 0-04. 



The hinge-plate and teeth are omitted for the present, as 

 the valves would not easily open and I was averse to using 

 pressure. 



Although T. tuberata, Jeffreys, with which I have com- 

 pared it, may be considered its nearest ally, it differs in several 

 essential respects from the species now under notice. T. 

 tuberata has no interstices between the ribs, and the latter are 

 crowded with cross bars, while T. papulosa has short and blunt 

 tubercles with spaces between, the sculpture resembling 

 Cardiiim papillosum. T. tuberata, again, is opaque and lustre- 

 less, while T. papulosa is crystalline white and semi-transparent. 

 Lastly, T. papulosa is more triangular in shape. 



J.C, v., April, 1887. 



