120 AnNAT.S OF TIIF. CARNEf;iK Ml'SKUM. 



Same Species in Other Localities. 



There are three si)ecimens in the museum collection from East 

 Bethany, N. Y., which are labelled C. Diiicronatiis but whose sharp, 

 distant strix and smooth umbos show that they belong to the species 

 here described. One is 6X8 mm. and has 20 striae ; a second is 

 6X9 mm. with 24 striae and the largest is 8 X 10 mm. and bears 

 22 strice and 4 pairs of spines. They are slightly less gibbous than 

 the Canandaigua Lake si)ecimens but are in other respects the same. 



On the beak and umbo of the ventral valve of one sj)ecimen are 

 growth lines marking the early stages. The smallest of these is 

 .35 mm. long and .41 mm. wide and the next is .65 mm. long and 

 .91 mm. wide. There is a narrow sinus which does not extend cjuite 

 to the second growth line but that line probably marks the limit of 

 the nepionic shell. It is slightly convex, and the hinge width is 

 about equal to the width below. 



The plications begin beyond a line 2.2 mm. from the beak. At 

 this stage the shell is 3.6 mm. wide, and the cardinal extremities are 

 a little extended. 



Chonetes : Summary. — All the species of Chouetes here described 

 have, as would be expected, the same general type of changes in de- 

 velopment. The different species are here compared at the various 

 stages. 



Frotegn/iim. — The shell in this stage is exceedingly small, but in 

 none of the specimens in the present material are the beaks well 

 enough preserved to show it. From Beecher's work we know that in 

 C. scituliis the protegulum is nearly circular in outline (.117 mm. 

 long and .111 mm. wide, according to the figure) with a strongly arcu- 

 ate hinge. 



Nepionic Stage. — The species agree in having the shell at this stage 

 convex in the ventral valve and convex at the umbo and concave (5r 

 flat in front in the dorsal valve. This is an advance on the condition 

 in Stropheodonta where the dorsal shell was convex during the whole of 

 the nepionic stage. 



The ventral valve always has a narrow sinus and the dorsal valve a 

 corresponding median fold and usually two less definitely marked 

 lateral folds. 



The outline issubcircular, though the width is usually a little greater 

 than the length. The hinge is somewhat arcuate. The length of the 



