PTEROPODA. 203 



CLATHROCffiLIA, n. gen. 



Among the fossils of the Hamilton group from Western New York are 

 two specimens of peculiar character, which do not appear to be properly 

 referable to any described genus within my knowledge. The general form, as 

 the fossil presents but a single face upon the surface of the rock, is that of a 

 small, flattened Orthoceras, or a longitudinal section of the same, with rapidly 

 expanding walls ; but a cursory examination shows that the two sides are not 

 equally diverging from the apex, one being in a nearly vertical line and 

 the other more oblique. The shell has apparently not been cylindrical, but 

 may have been of a flattened, triangular or semi-conical form. The interior 

 is marked by regular arching bands, which, as seen through the translucent 

 shell, have the appearance of septa. These septa are unequally arched, the 

 longer limb of the arch extending to the more sloping side of the shell, while 

 the shorter limb extends to the straighter side of the shell, and, before reaching 

 the margin, is recurved, and turns slightly backward or towards the apex. 

 The straighter margin is likewise a little recurved towards the exposed face of 

 the fossil. The latter feature, however, may be due to compression. 



The slight recurving of the septa resembles, in a considerable degree, the 

 arching of the chambers in the septate sheath of Phragmothec.a Bohemica of 

 Barrande ; but our specimens are rigidly straight, and possess other features 

 not conforming to that genus. Besides the arching, transverse lines or septa 

 there are several, at least four or five, longitudinal lines or laminae, which cross 

 the others, and apparently penetrate the interior in like manner. These 

 longitudinal lines give to the space included between the two central ones in 

 the upper part of the shell the appearance of a siphuncle, but they are in 

 nowise different from those on either side; and this apparent condition is 

 modified as the lines become less conspicuous towards the aperture of the 

 shell. 



In the obliquely arching outline of the aperture, this fossil is somewhat 

 similar to some forms of Hyolithes ; but the character of the shell and the 



