QO^GRYLIA—DITHYRA. 23. 69 



Dillwyn, Descript. Catal. p. 140. 



Turton, Concb. Diet. p. 81. 

 Mactra subtruncata. Donovan, Britisb Sbells, iv. tab. 126. 

 Trigonella zonaria. Da Costa, p. 197, tab. 15, fig. I. 

 Pectunculus cra.s.siusculus. Lister, Conch, tab. 253, fig. 87. 

 Mus. nost. From Teignmouth and Scotland. 



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

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

 more elongated and erect. 



Mactra testa ovato-trigond inwquilaterali, latere altera truncato, altera crassa. 



proclucto incurvo, umbonibus incurvis. 

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

 duced and incurved, beaks incurved. 



Tab. nost. 5, fig. 7. 

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

 Mus. nost. Dredged uj) in the Irish Channel. 



Shell two inches long and broad, and more than an inch high, 

 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 jn-oduc- 

 ed and rounded with an incurved slope from the hinge : beaks ^joint- 

 ed, much turned inwards and inclining towards the longer side : 

 teeth strong and prominent. 



Lister appears to have been well acquainted with this shell, 

 from the very exact description he has given of it — "Hwc testa 



