356 INTEODUCTION TO CONCHOLOGY. 



appendage; and the sinus in the muscular impression is 

 also wanting. 



Eew specimens have yet been discovered of the genus 

 MyocTiama, of which the shelly like that of Anatina, is fur- 

 nished with a testaceous appendage; and^ as in that of 

 Chama, the lower valve is fixed on some marine sub- 

 stance. The shell is inec[uivalve and irregular^ with two 

 diverging cardinal teeth in each valve, in the centre of 

 which is a triangular cavity, containing the small accessory 

 abeady noticed, and connected with it by a horny cartilage. 

 One valve is attached and flat ; the other free and convex, 

 covered with ribs or interrupted grooves, radiating from the 

 umboes. The ligament is thin and external. 



The genus CleidotJianis approximates to the above, in 

 having a similar appendage, and in being affixed by the 

 lower valve. The shell is inecjuivalve, somewhat pearly 

 internally : — the attached valve is convex ; the other flat, 

 with a small pointed tooth, fitting into a corresponding pit 

 in the former. 



Many of the preceding species are varied with bright 

 colours, and elaborately adorned; yet some of the most 

 brilliantly tinted dwell deep in the world of waters, occa- 

 sionally even in marine caves, or m fissures of rocks. 



