llCi AXNALS OK THE CARNEmE MuSEUM. 



the strife are introduced in this species. A ventral valve 1.41 by 

 1.59 mm. has seven strice, one of which originates on the median line 

 somewhat later than the others. A larger specimen, 1.72 X 2.06 mm., 

 has nine striae. A dorsal valve of about the same size, 1.72 X 2 mm., 

 has eight striai, two of which, in the middle of the valve, are longer 

 than the others, but do not seem to join the median fold of the 

 nepionic shell. After this stage more striae are added at the lateral 

 margins and, occasionally, by bifurcation and implantation, but the 

 number is, at all stages, very irregular. One specimen, 3 X 4. 23 mm., 

 has 14 striae, while one, 4.30 x 5.61 mm., has only 9. In the adult 

 stage there are from 25 to 40. 



Hinge Characters. — The area on both valves is narrow, that of the 

 dorsal valve being about one half as wide as the other. In all stages 

 the delthyrium is closed by a convex deltidium which covers about 

 two thirds of the opening. The chilidium on the dorsal valve is 

 nearly as wide as the greatest width of the cardinal area. 



Muscle Scars. — In the ventral valve are the two large flabelliform 

 scars of the diductors and between them the smaller adductor scars. In 

 the dorsal valve, just anterior to the cardinal process, are two small oval 

 scars, and, between them, a pair of slightly larger scars separated by a 

 low rounded septum. In front of these adductor scars are large 

 brachial areas which extend nearly to the anterior margin of the shell. 

 Each brachial area consists of two parts. On the outside there is a 

 rather strongly marked reniform impression which begins just outside 

 the muscular area and extends around to the front of the shell. Within 

 the crescent formed by this impression is a raised portion, which is 

 smooth and limited on its inner side by a ridge. 



These ridges originate at the sides of the median septum at about 

 the middle of the muscular area and extend three fourths of the distance 

 to the front of the shell, diverging at only a small angle from the 

 median septum. At their anterior ends they are usually high and 

 sharp, terminating rather abruptly. 



Cho7ietes scitulus and C. coronaius have the same markings on the 

 interior of their dorsal valves, but they are less deeply impressed. In 

 C. coronatus the middle (anterior) pair of muscle scars are long and 

 narrow, while the outer pair are larger and roughly rectangular. The 

 brachial areas can hardly be divided into two elements in the majority 

 of the specimens of this species, and in the young individuals no 

 impressions at all can be made out. 'I'he diverging ridges on each 



