3. 



COSC\UU\—DITHYRA. 23. 69 



Dillwyn, Descript. Catal. p. 140. 



TurtoH, Conch. Diet. p. 81. 

 Mactra subtruncaita. l}ouorttn, iv. tab. 126. 

 Trigoiiella zoimria. Da Costa, p. 19T, t;ib. 15, fig. 1. 

 Pectunculus crassiusculus. Lister, Coiitli. tab. 253, fig. 87. 

 3Iits. nost. From Teiiin mouth and Scotlaiul. 



Shell the size of the last, but is hardly as broad at the inargiu 

 as it is long at the sides which are more truncated, and the beaks 

 more elongated and erect. 



Mactra testa ovaio-trigonci tiicequilaferali, latere altera tnm- cra«a 



cato, altera producto incurvo, umbonibus inciirris. 

 Shell oval-triangular equilateral, one side truncate, the other 

 produced and incurved, beaks incurved. 

 Tab. nasi. 5, fig. 7. 

 Lister, Anim. Angl. p. 174, tab. 4, fig. 24. 

 3Ius. nost. Dredged up in the Irish Channel. 



Shell two inches long and broad, and more than an inch hi<^h, 

 very thick strong and solid, nearly smooth with a few antiquated 

 ridges about the margin, of a brownish color, abruptly truncate 

 on one side where there is a deep impression under the hinge 

 which is strongly and regularly striate obliquely, the other end 

 much produced and rounded with un incurved slope from the 

 hinge: beaks pointed, much turned inwards and inclining to- 

 wards the longer side : teeth strong and prominent. 



Lister appears to have been well acquainted with this shell, 

 from the very exact description he has givea of it — " Hac testa 



