PALEONTOLOGY. 459> 



length of the valve, and a little nearer the anterior than to the posterior end of the 

 carapace. Margin of the valves bordered by a narrow, elevated, thickened rim, 

 •which is expanded considerably in width around the anterior end of the valve, and 

 terminates in a rounded, elongated ridge at the posterior extremity of the hinge ; 

 from which point the ridge is directed obliquely forward and slightly downward 

 from the caudal line. The surface of each valve is divided into three slightly 

 elevated areas, with depressed sulci between ; an anterior, a central, and a posterior 

 one. The first is situated in the middle of the anterior end of the shell ; the cen- 

 tral one unites with the anterior one below, and extends along the basal margin be- 

 hind, in a narrow curved point below the posterior one, and projects upward near 

 the centre of the valve in a triangular form, terminating in an elevated point just 

 above the median line. The posterior and largest area is ovate in form, and occu- 

 pies a little less than one-half the length of the shell, is narrowed in front and 

 pointed behind, taking the form of the extremity of the shell. The centre of the 

 anterior area is slightly tumid. Along the hinge-line and just below its margin 

 there are three sub-angular tubercles or nodes, at nearly equal distances and of 

 nearly equal strength, except that the posterior one is prolonged at its base into a 

 low, rounded, and slightly curved elevation, which extends to near the point of the 

 central raised area before mentioned. These three nodes, together with the 

 oblique ridge-iike one terminating the marginal rim, border the hinge-line on each 

 valve. General surface of the valve finely punctate, but most distinctly so on the 

 posterior field. » 



The elongated form of the carapace readily distinguished this from 

 any of the other species described, while the number of node-like ridges 

 is a very marked feature. The abdomen and telson of this species have 

 not been observed, although several imperfect carapaces, mostly showing 

 parts of both valves, have been obtained. ' 



Formation and Locality. — In calcareous concretions in the Erie 

 shales, at Deroy, Lake county, Ohio. 



DECAPODA. 



Associated with the specimens of Entomostraca, described from the 

 concretions of the Erie shales of Ohio, are the remains of a Macrouran 

 Decapod, which appears to differ so much from any described genus as 

 to make undesirable to refer it to any of them. One of the peculiarities 

 consists in the possession of a pair of very strong antennal appendages, 

 which projects from beneath the anterior end of the thoracic carapace, 

 and are of such size and strength as to raise considerable doubt as to 

 their true nature. The existence of five thoracic limbs, exclusive of 

 these, projecting from beneath the carapace on one side would seem to 

 place their pedal nature out of the question ; while their great develop- 

 ment as seen on the specimen would indicate that they had served some 

 purpose other than simple antennae, and to raise the question as to the 

 possibility of their having been chelate at their extremities. As only 

 the basal portions of these organs are represented, however, this question 

 cannot be satisfactorily determined. Having had an opportunity of con- 

 sulting Dr. A. S. Packard, Jr., in regard to them, he gave as his opinion, 

 that from their position and the representation of the other five pairs of 



