250 Annals of the Carnegie Museum. 



opposite valve an equally abrupt sinus. The surface is usually smooth 

 but perfect valves show numerous fine wavy striae, crossed by still 

 finer concentric lines of growth. No interiors have been seen, but 

 in transmitted light pedicle valves preserved in calcite show the 

 spondylium. A perfect specimen has the following dimension: length 

 of pedicle valve, 7 mm., width, 5 min.; length of brachial valve, 5.5 

 mm. A larger brachial valve is 7 mm. in length and width, and a still 

 larger pedicle valve is 10 mm. long and 7.5 mm. wide. 



Locality. — This species is common in the middle of the Chazy at 

 Crown Point, Valcour Island, and Chazy; in the lower portion at 

 Valcour, and in the upper part at Valcour Island. 



34. Camarella varians Billings. 



(Plate XXXVI, figures 19-27, 33-36.) 

 Camarella varians Billings, 1859. Canadian Naturalist and Geologist, Vol. IV, 



p. 445, fig. 24. 

 Camerella varians Billings, 1863. Geology of Canada, p. 127, fig. 52. 

 Catnerella varians Billings, 1865. Paleozoic Fossils of Canada, Vol. I, p. 220. 



No name could be more appropriate for this exceedingly variable 

 species than the one proposed by Billings. Fortunately, a sufificient 

 amount of material has come to hand to enable us to trace the changes 

 which take place during the growth of this shell, and it will be shown 

 that the various varieties represent stages in the life history of the 

 individual. It is interesting to note that while at one stage in the 

 ontogeny the shell has a simple fold and sinus, without plications, 

 yet this shell does not correspond to Camarella longirostris, as the 

 pedicle beak does not project beyond that of the brachial valve. 



Ontogeny. 



The material which illustrates the ontogeny of this species consists 

 of a great number of perfect calcified specimens from the gray, coarsely 

 crystalline layers in the reefs at Smugglers Bay and Sloop Island, 

 Valcour Island, New York. The horizon is at the base of the Upper 

 Chazy. The specimens are not preserved in such a way as to throw 

 any light on the development of the internal structures, but the series 

 of stages in the growth of the external shell is complete from speci- 

 mens I mm. in length up to those 13 mm. long. 



In the nepionic stage the shell is elongate-oval in outline, the hinge 

 line shorter than the greatest width, both valves slightly and evenly 



