CONCHY U\—DITHYR A. 4. 21 



hinge near one end where it is rounded ; the other end truncate 

 and open nearly half way across, with often three or four longitu- 

 dinal laminar ridges on the inside : this side is also more or less 

 angular, in consequence of a raised ridge extending from the 

 beak to the end, and which is often a little rough like theHiatella 

 minuta. 



The valves are sometimes pressed close together at the trun- 

 cated end, causing the opposite or rounded side to open widely, 

 in which state it has much the appearance of the Gastrochaena 

 pholadia, and we have observed it marked as such in cabinets; 

 but attention to the following particulars will always distinguish 

 it. The elongated side is truncate ; it wants the small laminar 

 teeth in the valves ; and on the back part at the rounded end the 

 valves do not meet together. 



Saxicava testii ovatd, transversim striata, extremitatibus rotun- Phoiattis. 



datis subhiantibus. 

 Shell oval, transversely striate, rounded and somewhat open at 

 both the ends. 



Tah.nost. 2, fig. 11. 

 Mytilus Pholadis, Linn. Mant. p. 548. 



Linn. Iter. Westgoth. tab. 5, fig. 2. 

 Ginelin, Syst. p. 3352. 

 Tnrton, Linn. Syst. iv. p. 295. 

 MuUer, Zool. Dan. iii. p. 12, tab. 87, fig. 1 

 to 3. 

 Mya byssifera. Fabricius, Faun. Groenl. p. 408. 

 Mus. nost. JRocks in Torbay. 



