250 MOLLUSCA FROM THE CRAG. 



MESODESMA JAURESII. De Joannis. Mag. de Zool. Moll., pi. 54, 1834. 



_ __ Gould. Invert. Massach., pi. 58, fig. 38, 1841. 



DEAURATA. Forb. and Hani. Hist. Brit. Moll., vol. i, p. 346, 1848. 



ERYCINA DENTICULATA. Cuvier. (Griffiths.) An. Kingd., t. 22, fig. 2. 

 PAPHIA DEAURATA. Gray. List Brit. Moll., p. 157, 1851. 



Spec. Char. Testa transversd, oblongo-ovatd, intequilaterali, crassa ; transverse striatd 

 vel snbimbricatd ; antice longiore et rotundatd ; postice truncatd ; cardine bidentato ; denti- 

 bus lateralibus magnis, striatis. 



Shell transverse, ovately oblong, inequilateral, thick and strong, transversely or 

 concentrically striated ; anterior side the longer, and rounded ; posterior truncated ; 

 lateral teeth large, and perpendicularly striated. 



Length, lj inch. Height, f inch. 



Locality. Red Crag, Button, Walton Naze. 



Recent, North-east Coast of America, Newfoundland. 



The specimen figured was found at Walton-on-the-Naze by John Brown, Esq., of 

 Stanway. There is another in my own cabinet, from the Red Crag at Sutton, but not 

 in quite so good a state of preservation. It may be thus more fully described : The 

 anterior side is much produced, the base line of the shell ascending towards the 

 extremity, where it is roundedly pointed, while the siphonal side is very short, and 

 obtusely biangulated ; the surface is covered with irregularly elevated lines of growth 

 or ridges ; corresponding with the figure and description given by Turton, who says 

 it somewhat resembles in outline M. dealbata, but differs in being thicker, and 

 also in the teeth, though he does not tell us what these latter are like in either 

 species. 



The recent shell is placed by some authors in the genus Mesodesma. A small 

 A -formed tooth is present in this left-hand specimen, placed immediately before a 

 large ligamental area, as in Mactra, with elongated lateral teeth, which are striated. 



LUTRARIA,* Lamk. 1799, 



MACTRA (sp.) Linn. 



PSAMMOPHILA. Leach, MS. 1819. Fide Brown. 



LUTRICOLA (sp.) De Blainv. 1824. 



Generic Character. Shell transversely ovate or oblong, inequilateral, and gaping 

 at the lateral extremities ; externally smooth, or slightly striated transversely. Hinge 

 with a prominent triangular or diverging tooth in the right valve, with a corresponding 

 pit for its reception in the left. Ligament internal, placed in a large spoon-shaped 

 depression in each valve. Impression by the mantle deeply sinuated. 



* Etym. Lutra? a luto, to daub, probably from its mud-like exterior. 



