PLASTOMENIDvE. 469 



No additional material having been discovered, we can do little more than reprint Cope's 

 description: 



Established on a costal bone found in association with the preceding species, and referred to the 

 genus Plastomenus provisionally, and with a probability that it will be found not to pertain to it when 

 fully known. That genus has so far only been found in the Eocene formation. The bone is rather thin 

 and sufficiently curved to indicate a convex carapace of moderate thickness. The surface is marked 

 with closely packed shallow pits without material variation of form on the proximal end of the bone. 

 The result is an obsolete sculpture quite similar to that seen in some species of the genus to which it 

 is at present referred. 



MEASUREMENTS. 



Meter. 



Width of costal bone o.ozjo 



Thickness of costal bone 0033 



Number of pits in o.oio meter, 6. 



Lignite Cretaceous of Colorado; also several fragments from Long Lake, Nebraska, from Dr. 

 Hayden. 



It will be observed that the pits of this carapace are small, and measurements made on 

 the specimen show that there are sometimes seven pits in a line 10 mm. long. The thick- 

 ness of the bone at the neural border is nearly 5 mm.; thru the swelling caused by the rib on 

 the under side, it is 5 mm. Cope's measurement was taken at the sutural border. 



The type locality being known, it does not appear necessary to despair of finding and 

 identifying other specimens of this trionychid. 



It is possible that this species belongs to the genus Plastomenus, but of this we can not be 

 assured before additional carapacial materials shall have been found accompanied by the 

 plastron. 



Plastomenus? insignis Cope. 



Plastomenus!' insignis, COPE, Ann. Report U. S. Geol. and Geog. Surv. Terrs., 1873 (1874), pp. 433,454; 

 Bull. U. S. Geol. and Geog. Surv. Terrs., I, No. 2, 1874, p. 29; Vert. Cret. Form. West, 1875, pp. 95, 

 261, plate vi, fig. io. HAY, Bibliog. and Cat. Foss. Vert. N. A., 1902, p. 452. HATCHER, Bull. 

 U. S. Geol. Surv. No. 257, 1905, p. 75. 



This species was based on a single fragment of the hypoplastron, presenting a part of the 

 free border of the hinder lobe close to the inguinal notch. This type belongs to the American 

 Museum of Natural History and has the number 1846. It is accompanied by a label in Cope's 

 handwriting as follows: "Plastomenus insignis. 10-9-1873, Colorado." In his description 

 Cope states that this specimen was found in the same locality as his P. punctulatus; and as 

 shown under the latter species, page 468, this locality was somewhere on BijouCreek, Colorado. 

 The formation is believed to be the Arapahoe. Professor Hatcher regarded the type locality 

 as doubtful, and this species as therefore worthless from a biological and a stratigraphical 

 point of view. There can be no doubt about the type locality, and the present writer believes 

 that it will be possible to identify other materials coming from this locality and having the same 

 part present. 



The fragment has a length of 23 mm. and a width of 1 1.5 mm. It extends forward to the 

 suture with the hyoplastron and backward nearly, if not actually, to the suture with the 

 xiphiplastron. The acute free border of the bone extends forward within io mm. of the 

 hyohypoplastral suture. This fact shows that the species must have been a small one, 

 perhaps not more than 150 mm. long. At the suture with the hyoplastron the bone is 4 

 mm. thick. 



Cope states that the suture with the xiphiplastron was gomphosial. At the hinder end ot 

 the bone there is a smooth pit which may have received a process from the xiphiplastron. 

 The writer can not convince himself that any other part of the suture is present. There 

 is no excavation of the free border for a forwardly directed process of the xiphiplastron, such 

 as we might have expected. 



The specimen affords no characters that confirm or that refute the reference of the species 

 to the genus Plastomenus. 



