112 AMPHIBIA AND PISCES OF THE PERMIAN OF NORTH AMERICA 



Measurements. 



Skull No. 4570 Am. Mus. Nat. Hist. : mm A femur, No. 4584 Am. Mus. Nat. Hist. : mm 



Length on mid line 122 Length 50 



Length to posterior end of lower Breadth proximal end 16.5 



jaw 139 Breadth distal end 17 



Greatest breadth Hi -S A second femur, same number: 



Distance from back of skull to Length 43 



middle of orbits 76 Breadth of distal end 14 



No. 4714 Am. Mus Nat. Hist.: Breadth of proximal end 12.5 



Length of lower jaw 180 Ilia: 



Greatest depth of ramus 31.5 Length of an average specimen 37 



Three humeri No. 4720. .No. i. No. 2. No. 3 Breadth of lower end 19 



Length 49 46 45.5 Breadth of lower end 13 



Width distal end 23 21.5 21.5 



Width proximal end. . 15 15 IS 



Trimerorhachis insignis Cope. 



The morphological desciiption of this species is contained in that of 

 the genus. 



Trimerorhachis conangulus Cope. (Plate ;, fig. 6.) 

 Characteristic specimen: Type No. 4569 Am. Mus. Nat. Hist._ Cope Coll. 

 There is some doubt whether this creature should be retained in the 

 genus, but it is better to leave it there until further knowledge is gained. 

 It is known from the skull only, and was identified by Cope as Trimero- 

 rhachis by the anterior position of the orbits and the united condyles. _ 



The original description is adequate. It is to be noted that an inter- 

 temporal is clearly shown or: both sides (fig. 8). As the sutures of the skull 

 in the typical specimens of the genus can not be made out clearly, it is 

 impossible to say whether this is a constant feature. 



Trimerorhachis mesops Cope (page 46). (Plate 12, fig. i.) 



Characteristic specimens: Type No. 4568 Am. Mus. Nat. Hist. Cope Coll. 



The original description points out the characters by which this species 

 may be distinguished from the other species of the genus. The specimen 

 is so imperfect that it does not permit of an accurate characterization. The 

 peculiar "sheet of matrix," mentioned by Cope, is the most interesting part 

 of the specimen. This is a wrinkled sheet composed of nunierous alternate 

 red and white layers, not over one-tenth of a millimeter thick. The white 

 layers are badly contorted and seem to be discontinuous; an attempt to 

 trace them for any distance fails. The layer is also apparently made up of 

 small, broken fragments, as if it had been originally a heavily calcified 

 tissue, sufficiently so to be brittle under pressure. A small fragment, ground 

 thin and placed under the compound microscope, was declared by Dr. 

 Huber, professor of histology in the University of Michigan, to present an 

 appearance in some places Tike that of epithelial cells, such as occur in horny 

 parts of the epidermis. It is possible that this animal possessed a unique 

 ventral armor made up of successive layers of heavy epidermis; this is ren- 

 dered more probable by the fact that no trace of the characteristic scutes 

 or rods, which form the abdominal protection of contemporary amphibians, 

 is found in the specimen. If the creature died and sank down upon some 

 fragment of skin from some other creature, the abdominal^ ribs would have 

 been preserved, but none are present. The plate of matrix is unique, and 

 future discoveries must determine whether it is an accidental association 

 or a peculiar feature of this animal. 



