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PROCEEDINGS OF THE NATIONAL MUSEUM. 



vol. 40. 



is 



to distinguish the one from the other. Parts of the plants have 

 been converted into or destroyed by galena and kaolin, as have 

 also parts of the bones, so that the task has been doubly difficult. 

 There can be no doubt, however, that the observations recorded 

 below are correct. The position of the arm in relation to the pec- 

 toral girdle and the position of the girdle in relation to the skull 

 impression first called attention to the possible presence of a fossil 

 amphibian. 



There is little to be said about the skull. It is merely an impres- 

 sion in the nodule. It is triangular in form, with the snout an acute 

 angle. The angle is, however, exaggerated by the compression to 

 which the fossil has been subjected. The right side of the skull lies 

 over a portion of some plant. The animal is pre- 

 served on its back, so that this gives a good oppor- 

 tunity for a study of the pectoral girdle, which 

 is partially preserved. The interclavicle is very 

 large, and from this the species has been given its 

 name (thoracatus = armed with a breastplate). 



/The interclavicle is an exaggerated "T," with the 

 stem very short. The anterior margin is curved 

 and ends in a rather sharp, elongate point. The 

 posterior spine is quite short and sharp pointed, 

 having a length of only four millimeters. The 

 element recalls, in a measure, the same element 

 of Branchiosaurus, although it is much more ex- 

 panded anteriorly and has a shorter spine. In 

 these respects it resembles more nearly a reptilian 

 interclavicle. The element is quite smooth. 



The clavicle is of the simple triangular form 

 so characteristic of the Microsauria. It is some- 

 what displaced backward, and its inner margin 

 is slightly obscured. 

 The humerus is elongate, apparently cylindrical, and with expanded 

 ends. It resembles very closely the humerus of Amphibamus grandi- 

 ceps, although its proportions are much greater than in that species. 

 Its length is almost equal to the length of the skull, while in A. grandi- 

 ceps the length of the humerus is only one-half that of the skull. 



The radius (ulna?) resembles in its general proportions those of 

 the humerus. It is a more slender, lighter bone. The impression 

 of the other bone of the forearm is obscured. 



A portion of a single vertebral centrum is preserved. It is from 

 the posterior end of the dorsal series. It is, apparently,- amphi- 

 ccelous. Its height is about one-half greater than its length. The 

 neural spine is obscured. 



'v 



Fig. 2.— Drawing of the 

 specimen of amphiba- 

 mus thoracatus 

 Moodie (Cat. No. 4306, 

 U. S.N.M.). c= Clav- 

 icle; ft = humerus; i = 

 interclavicle; o= or- 

 bit; r= radius (ulna?); 



V= VERTEBRA. X 1. 



