Page:Second Geological Survey of Pennsylvania Report of Progress PPP.djvu/44



Carapace unknown. Body elongate, very convex along the dorsum, composed of twelve free segments which gradually increase in breadth from the head backwards to the fifth somite, from whence they rapidly decrease in width and increase in length, until the eleventh segment has a length equal to half its width, while in the fifth segment the breadth is four times its length. Lateral margins of the segments flattened, and slightly extended backwards on the post-lateral angles, forming a mucronate projection. The posterior tergal margin of each somite is ornamented with several triangular scales or nodes, pointing towards the telson. The number of these nodes on each segment decreases from the anterior segment, which has eight or more, to the tenth somite which is furnished with six. The number on the two posterior segments is not known, on account of their imperfect preservation in the specimen described.

Two joints of one of the great swimming feet are preserved, which are remarkable for their great length and for three or more strong longitudinal carinæ ornamenting them. The distal joint of the two has a length of more than three times its breadth, while the other has a length of nearly five times its breadth. These joints are probably the third and fourth from the attachment of the limb and correspond to the basos and ischium of a typical decapod. Telson and other appendages unknown.

The twelve free segments of the body have a total length of 96 mm., and the width of the fifth segment is 41 mm. The body measures 39 mm. across at the first segment and 25 mm. at the tenth. The longer joint of the natatory appendage has a length of 30 mm.

The specimen from which the present description is taken was found in a bed of fine grained sandstone occurring in the Chemung group at Warren. Although lacking many of