]^4 PROCEEDINGS OF THE XATIONAL MUSEUM. vol.37. 



and the two phalanges. The elements of the other three digits are 

 scattered so it is impossible to determine exactly the phalangeal 

 formula for the hand, though it may have been 2-2-3-2. 



The pelvis is represented by portions of the ilia which are ex- 

 posed. The ischia and pubes are not visible. The ilium of the left 

 side is the better preserved. It is seen to be an elongate, flattened 

 plate slightly curved to accommodate the head of the femur. Two 

 sacral vertebra gave support to the ilia, possibly through the inter- 

 vention t)f sacral ribs. 



The hind limbs are very strong, with the foot much expanded and 

 the tarsus well developed and bony. The femur is especially strong, 

 and recalls in its proportions some of the higher reptiles. Its head 

 is a little obscured through crushing, but the articular surface for the 

 ilium seems to have been quite large, covering at least an arc of 40°,^ 

 and thus indicating a wide range of movement for the leg. The two 

 ends of the bone are expanded, but there are no tuberosities for mus- 

 cular attachment nor should we expect any. The articular surface 

 of the distal end is divided into two clearly marked facets for articu- 

 lation with the tibia and fibula, recalling in this respect the femur 

 of the plesiosaurs. The tibia has a triangidar head, a contracted 

 distal end, and a slender shaft. The fibula is slightly curved with the 

 ends expanded. The distal end is wider than the proximal. 



The tarsus, as preserved, in the left foot is composed of eight ele- 

 ments — two ])roximal and six distal tar:-a]ia, one of which may be a 

 sesamoid or a fractured portion of " t 5." The astragalus (tibiale) 

 and calcaneum (fibulare) are both rounded, but with articular facets 

 for the accommodation of the tibia, fibula, and distal tarsalia. There 

 is no evidence of a centrale carpi or intermedium. The carpus is 

 quite regular, and shows more specialized characters than do the later 

 Cotylosauria, in which the centmle is still present, in one species of 

 Lahidosaurus at least. 



The digits of the foot are long and slender, with a progressive in- 

 crease in length from the first to the fourth. The fourth and fifth 

 are 'nearly equal in length. The metacarpals of all five digits are 

 long and exhibit full ossification, though no evidences of epiphyses 

 are present. The terminal phalanges are pointed. The phalangeal 

 formula of the foot is 2-8—1—5-4, a typical reptilian arrangement. 

 In closing his discussion of this species Cope says: "This specimen 

 is of importance as pertaining to the oldest known reptile, and the 

 only one wdiich has thus far been positively identified from the Coal 

 Measures. I announced this identification in the American Natural- 

 ist, 1896, page 303." 



The absence of ventral ribs is an assured character in Isodectes. I 

 have searched for them under high power of magnification, and have 



