346 Description of several new Trilohites. 



they occur is a ferruginous clay slate, filled with other petrifactions. 

 My friend John F. Frazer, Esq. informs me that the geological 

 structure of Huntingdon and its vicinity, belongs to the classification 

 of rocks, called by Professor Rogers, in his annual report as State 

 Geologist, the olive slate stratum. This stratum reposes on a coarse 

 grained sandstone, full of organic remains, and is thus described in 

 the report. 



" The next stratum is a dull olive colored slate, alternating with 

 grey argillaceous sandstones. Towards the upper portion some of 

 the layers consists of a soft, very yellow slate, which increases as 

 we ascend, becoming, in the upper part, the principal variety. It 

 alternates with beds which gradually assume a brown and reddish 

 tinge, that grows gradually more distinct, indicating the gentle passage 

 of this rock into the red argillaceous stratum above it. The inferior 

 layers contain occasionally large deposits of a very argillaceous iron 

 ore, approximating in its composition and characters to the argilla- 

 ceous iron stone of the coal measures. This stratum abounds also 

 in mineral springs, the predominating ingredient of 'rhich is sulphu- 

 retted hydrogen. It may for convenience sake, be called the olive 

 slate stratum." 



Cryph^us Collitelus. Green. 



Cauda utrinque in lobis quinque divisa ; lobis elongatis, rectis, 

 acutis. 



I have seen the caudal end only of this exceedingly interesting 

 trilobite, but it differs so much from the other species described, that 

 there is little doubt of its being distinct. There are eleven or twelve 

 articulations of the vertebral column, and but five of the costal arches 

 of the sides visible in our fragment. The joints of the middle lobe 

 of the back are narrower, more numerous, and by no means so prom- 

 inent as those of the C. Boothii, and the terminal joint is also much 

 smaller. The costal arches or ribs of the sides are remarkably broad, 

 and are strongly marked by a deep sulcus running along their infe- 

 rior edge ; they commence at the seventh joint of the vertebral col- 

 umn. The scollops or leaf-like lobes of the tail are five in number, 

 and are remarkably large in proportion to the body of the animal ; 

 they form a regular continuation of the last five arches of the sides, 

 and terminate in free points, without any curvature. A thin rib 

 passes from the tip of each lobe through its middle to the sides of 

 the animal, probably for the purpose of giving strength to the large 

 development of the membrane. The body of the animal is broad. 



