'rkoi'iiioi.i.i'irs Faina at ('AXAXUAKa'A Lake, N. Y. 119 



smooth character extends for a length of only i mm. and there are 

 many specimens which are between these limits. 



In the earliest plicated stages seen, there are 12 striae on the dorsal 

 valve and 13 on the ventral. One specimen showing this stage is 

 5.15 mm. long and 6. 38 mm. wide. The striae are all simjile and 

 the ones in the middle are longer than those on the sides. Other 

 smaller specimens show this same number, or, in some cases, more 

 stri.x. A specimen 1.93 x 2.92 mm. shows 15 striae. A dorsal 

 valve 5.13 X 7.66 mm. shows 16 simple stri;i;, and a ventral valve, 

 6.46 X 7-93 mm. has 19. On specimens larger than this new striae 

 are added by bifurcation or by the implantation of new striae between 

 older ones. The highest number on any of the shells was 36 and the 

 usual number for adults is 20 to 30. 



Character of Hi/ii^e. — The area of the ventral valve is narrow in 

 the adult, but about twice as wide as that of the dorsal shell. The 

 deithyrium is rather narrow and is completely covered by the slightly 

 convex deltidium. A pedicle opening can be seen in one or two of 

 the adult specimens. On the dorsal valve there is a chilidium pos- 

 terior to the dental sockets and cardinal process. 



Muscle Scars. — ■ In the ventral valve are the large, flabelliform im- 

 pressions of the diductor muscles, and the narrow, elongate adductor 

 scars. In the dorsal valve the middle pair of adductor scars are elon- 

 gate oval, and situated on a sort of platform just in front of the car- 

 dinal process. On either side and at a lower level are the rounded 

 outer scars. The brachial impressions are large and rounded and their 

 limit is marked by a single row of pustules. The medium septum and 

 the two lateral ridges are faintly marked. 



Spines. — Owing to the small number of ventral valves the position 

 of all the spines could not be determined as satisfactorily as with the 

 other s{>ecies. Ten specimens were measured and the averages are as 

 follows: 1st pair, .47 mm. from beak; 2d, .96; 3rd, 1.29; 4th, 

 2-03 ; 5th, 3-3° ; 6th, 4.24 ; 7th, 5.61 ; 8th, 6.16 ; 9th, 8.33. Thus 

 if all the sjjines were developed on one individual, there would be 

 nine pairs, but the specimen in this collection which bore the greatest 

 number had only six pairs and the majority of them had only 4 or 5 

 pairs. The spines stand out at about the same angle with the hinge 

 as do those of C. coronatiis. The limits were 21° and 40°, but the 

 average w^as above 30°. 



