BEEKMANTOWN AND CHAZY FORMATIONS OF CHAM PLAIN BASIN 41 1 



Camcroceras curvatum sp. nov. 



Plate 2, figure 6, 7 



Description. Medium sized cyrtoceracones with extremely closely 

 arranged septa and large, marginal siphuncle. The size attained 

 by the mature conch is unknown ; the fragment which is the type 

 of the species has a length of 62 mm but its rate of growth which 

 is 8 mm in 62 mm (17 mm at smaller diameter and 25 mm at 

 larger diameter) indicates a missing apical portion of 120 mm, 

 and the living chamber is also missing. The type specimen can be 

 said to have had a length of approximately 200 mm. The curvature 

 is slight (the hight of the arc of the fragment is 3 mm) and a 

 little stronger in the apical than in the anterior part of the conch. 

 The section of the conch is circular. 



The cameras are exceedingly shallow ; there being counted 9 of 

 them in the space of 20 mm in the type specimen. The sutures 

 have been observed only in part and a narrow high saddle on the 

 inner side of the conch has been noticed. The septa are very thin, 

 advancing considerably on the convex side of the phragmocone 

 and their depth is thrice that of the cameras. The shell is thin and 

 not only the siphuncle but also the chambers 

 appear to have become partly filled with 

 organic deposit. 



The siphuncle, which is tubular and exactly 

 two fifths the width of the phragmocone, is in 

 contact with the wall at the inner side of the 

 curve [see text fig. 2I. The endosiphocone . 



L 1 Fig. 2 Lameroceras 



is very long and slender (^0 mm) and the curvatum sp. nov. 



- 7 fe \0 / Transverse seen n. x r 9 „ 



endosiphosheaths are correspondingly long 



conical in shape. The endosiphotube is well developed. The 



septal necks end upon the geniculations of the preceding septa. 1 



Position and locality. In the dove-colored Chazy limestone (Q) 

 of Isle La Motte (loc. 215, Professor Perkin's coll. ; type in the 

 collection of Burlington University). Its presence in the same hori- 

 zon at Valcour and Chazy in New York can hardly be doubted, but 

 the fragility of the shell renders it one of rare observation. 



Observations. This peculiar form shows, if we disregard the 

 curvature, an extreme development of some of the characters of 



1 The structure of. the siphitncular wall, described under E. opple- 

 t u m, is also here observable; notably the presence of a slight interspace 

 between each septum and the termination of the septal neck of the fol- 

 lowing septum. 



