COSCBYUX—DITHYRA. 1. 



Wood, Conch, p. 81, tab. 15, fig. 3 to 5. 



Dillwyn, Descript. Catal. p. 40. 



Turton, Conch. Diet. p. 146. 

 Pholas bifrons. Da Costa, Brit. Conch, p. 243, tab. 16, fig. 4. 

 Pholas latus. Lister, Conch, tab, 436. fig. 279, and Append. 



tab. 19, fig. 3. 

 Mus. nost. In rocks and hard clay. 



Shell usually an inch and a half long, and two in breadth, 

 whitish or ferruginous, much thicker and stronger than the other 

 species, rounded at the hinder end and produced into a short 

 beak at the other : from the middle of the hinge runs a longitu- 

 dinal groove, dividing the valves into two nearly equal portions, 

 the anterior or more produced portion marked with strong trans- 

 verse muricate striae on the outer surface, the other part marked, 

 with plain and rather obscure ones : hinge smooth, and without 

 any elevated process on the margin above the teeth. In conse- 

 quence of the length being nearly equal to the breadth, the valves 

 have a somewhat triangular appearance, causing both the extre- 

 mities to be very open. 



Lister, in his appendix ad Hist. Anim. Angl, p. 44, observes, 

 that there is a small accessorial valve at the hinge: " kuic quod 

 imprimis notandum est, etiam tertia testa exigua est ad vaha- 

 rum cardinem." And Linne Mus. Reg. Lud. Ulr. p. 469, makes 

 the same remark, taking Lister for his authority: " accessoria 

 tertia ad cardinem exigua, Lister, hujus idioque generis.^' We 

 kave not as yet been fortunate enough to find it in its native 

 lodgement. 



