CLINTON GKOUP. 183 



rest, on one side, upon the costal plates. The costal plates are, with one exception, all modified 

 in form ; and just beneath the ovarian aperture, a supernumerary plate is intercalated. Or 

 the plate a may perhaps be regarded as a scapular plate, or a plate of the third series, 

 developed between two plates of the second series, and supporting as do the adjoining third 

 plate on one side and second plate on the other side, the arms as shown in the figure. 



This is doubtless an abnormal development, and can not constitute any specific distinction. A 

 less important deviation has been observed in another specimen, but it is clearly due to a similar 

 cause, or to some accident at one period of the animal's growth. 



Position and locality. In the upper limestone of the Clinton group at Lockport. 



i^Colleclion of Col. Jewett.) 



577. 2. TENTACULITES MINUTUS. 



Pl. a XLI. Figs. 8 a - e. 

 Tentaculites minutus. Hall,, Geol. Rep. 4th Dist. N. York, 1843, p. 72. 



Tubes single, straight, rigid, minute, annulated ; annulations extending to the apex, obtuse 

 or rounded, distant three or four times their thickness ; intermediate spaces smooth. Length | 

 of an inch. 



This little tentaculite is found in the green shale ; and from being extremely minute, its 

 characters are not always well preserved. In length it is from one-eighth to three-sixteenths of 

 an inch, and is marked by from fifteen to twenty annulations. I am unable to distinguish either 

 longitudinal or transverse striae between or on the annulations. In two specimens measured, 

 there are seventeen annulations in the eighth of an inch. The annulations are usually sharp rings, 

 rising abruptly from the tube, and comparatively distant from each other. 



Fig. 8 a. A small fragment of the green shale, preserving several specimens of this fossil. 



Fig. 8 b. Two specimens drawn separate from the shale, of the natural size. 



Fig. 8 c. An individual enlarged. 



Figs. 8 d, e. Portions of two individuals still further magnified, showing in one an apparent 



crenulation of the rings. 



This feature is observable in two or three specimens, but it is difficult to make it 



out clearly ; while in others the rings are decidedly plain. This difference may be due 



to the presence or absence of the outer crust or shell. 



Position and locality. In the upper green shale at Rochester, associated with Atrypa hemi- 

 Spkerica. {State Collection.) 



