224 Annals of the Carnegie Museum. 



Camarotxchia orientalis and Hebertella borealis are found with a pro- 

 fusion of cystids of tfie type of Malocystites mnrchisoni. In the cor- 

 responding fauna at Valcour Island, Camarotcechia plena and Heber- 

 tella vulgaris occur with other cystids, the most common of which is 

 Malocystites emmonsi. Malocystites murchisoni does not occur in 

 the same layers, but is quite common some hundreds of feet lower in 

 the strata, below the range of Camarotcechia plena. 



In the Aylmer formation at Aylmer, Camarotcechia orientalis occurs 

 in the sandstone at the base of the section, accompanied by Hebertella 

 impcrator. The specimens of Camarotcechia orientalis in the sandstone 

 are casts, and the divided septum in the dorsal valve and the absence 

 of a cardinal process show that the shells are Camarotcechias. 



Ontogeny. 



For comparison with Camarotcechia plena a short sketch of the life 

 history of this species is introduced. 



1. Nonplicate nepionic stage of short duration. Shell biconvex, 

 smooth. 



2. First (reversed) neanic stage. With the introduction of the 

 first plication on the pedicle valve, a sinus is formed on the brachial 

 valve, and this state, in which the normal form of the adult is reversed 

 ■continues until the shell reaches a length of from 3 to 5 mm. When 

 the shell reaches this size all the plications of the adult, nine to fourteen, 

 can be detected on the anterior margin. The pedicle valve is then 

 deeper than the brachial, the ventral beak is a little incurved, and the 

 delthyrium is open. 



3. Equivalve neanic stage. After the shell reaches a length of 

 from 3 to 5 mm., the dorsal sinus becomes gradually shallower and 

 finally disappears, and the ventral fold merges into the uniform ro- 

 tundity of the front of the shell. When the shell reaches a length of 

 from 7 to 8 mm. the two valves are about equally convex and the fold 

 and sinus have disappeared. 



4. Normal adult stage. The next change is the formation of a 

 •dorsal fold and a ventral sinus. This change takes place gradually 

 and the shell does not show the adult condition until it has attained 

 a length of 10 or 12 mm., although it acquired all its plications when 

 only 3 or 4 mm. long. In the adult state there are four plications 

 on the fold and three in the sinus. 



