236 PROCEEDINGS OF THE ACADEMY OF 



Adocus petrosus Cope. 



This species is represented by portions of four costal bones, parts or wholes 

 of six marginal bones, most of the right hyosternal, and a posterior portion of 

 the right hypostenial, with the head of the os coracoideum. They were found 

 in the West Jersey Marl Company's pits, Gloucester Co., N. J., in the same lo- 

 calitj' whence the Laelaps was procured. 



The hyosternal bone is preserved in its axillary margin, and is continuous 

 with two marginals of the carapace of the same side. Two of the costals are 

 adjacent, and give the outlines of the vertebral bones and scutes. These show 

 the inferior outline to be very convex, the whole, from angle to angle of the 

 marginal bones of opposite sides, amounting to an arc of about 124 degrees. 

 Each hyosternal is slightly concave below the plane of their comdon suture. 

 Each thins out laterally, though the one preserved is very thick on the axillary 

 margin. There is little difference between the thickness at the mesostertial 

 and hyposternal sutures. All the sutures have minute rugosities, differing much 

 from sternals in A. a g ills and Taphrosphys, which are very ragged, and re- 

 sembling those of Pleurosternum p e c t o r a 1 e m. The piece of hyposternal is 

 even thicker than the hyosternal. The bone is everywhere remarkable for the 

 thickness of its dense layer, and the closeness of the texture of the spongy. 

 The former is one-third the thickness of the sternal and costal bones frac- 

 tured. 



The scute sutures of the inferior surface are obsolete ; those of the dorsal 

 surface are like those of Adocus, i. e., the vertebrals with bracket-shaped 

 lateral borders, with the costal proceeding from the point of the bracket. 



The marginal bones vary much in thickness proximally. They have two 

 proximal sutures, one side convex, the other concave. Four have a heavy bor- 

 der, round in section ; in two of these it is considerably everted. Another has 

 a rather thin margin, slightly decurved, with a submarginal groove separating 

 it from the most massive portion. The costal bones are strongly convex in 

 their length, indicating an arched carapace. 



3Ieasure7nents. 



In. Lin. 



Hyosternal Avidth ,, 3 9 



" " to origin axillary abutment 2 1-5 



'• length on median suture 2 1-5 



" thickness near mesosternal line 9 



" " " hyposternal " 7-2 



Hyposternal thickness near posterior suture 9 



Costal width , 1 7-5 



" thickness vertebral suture 8 



Marginal No. 1 width 2 1-5 



" " length 1 7 



" " proximal thickness , 3 



" No. 5 " " . 8-2 



" " length 1 6 



" " wadth 1 7-5 



" " width dermal scute >. 9 



This animal is therefore a species of considerable size, though less than most 

 of 'those described here, and particularly convex and solid in every part, While 

 the sutural lines of the hyosternal measure about the same as in A. firmu s 

 (Emys Leidy), it is much more convex and not so thick at the mesosternal 

 suture. The marginal bones are relatively just half the size. The Pleuroster- 

 num i> e c t r a 1 e ditfers in being very much flatter, and in having a more 

 discoid mesosternal bone. The hyosternals are also much thicker at their 

 union with the marginals than in the present. 



A portion of a hyo- or hyposternal bone collected at the same place, and 

 near or at the same time, may be referred to a larger individual of the same 



[Oct. 



