202 PALEONTOLOGY. 



gosaurus presents in its persistent notochord, cartilaginous 

 basi-occipital, dermal ossifications on the head, and minute 

 body-scales (fig. 84, scales), remove it further from the saurian 

 reptiles, and exhibit it more strongly in the light of a transi- 

 tional form between the Batrachians and the Ganoids. 



The under surface of the body between the head and trunk 

 is defended by broad bony plates, three in number. One is 

 median and symmetrical, of an elongate lozenge shape, with 

 the angles rounded of; the outer surface is sculptured by 

 radiating furrows, except at so much of the marginal part as 

 is overlapped by the lateral pieces, and by the scapular arch. 

 The lateral throat plates are attached to the anterior half of 

 the sides of the median one, are shaped like beetles' elytra, and 

 converge forwards. Their centre of ossification is towards 

 their outer and back part, from which the external ridges and 

 grooves radiate towards the inner border. 



Von Meyer* compares these dermal shields to the ento- 

 and epi-sternal elements of the plastron of Chelonia ; their 

 truer homology seems to the writer to be with the median and 

 lateral large throat-plates or scales of Megalichthys and Sudis 

 gigas. The ento-sternal element is the only endo-skeletal piece 

 uncombined with a dermal ossification in most Chelonia ; in 

 which order the epi-sternal, like the hyo- and hypo-sternals, ap- 

 pear to be abdominal ribs, with superadded dermal ossifications. 



The scapulas (fig. 84, 51) are short and straight, with the 

 upper free end inclined " forward toward the occiput. The 

 coracoids (52) are represented by a pair of flat reniform plates, 

 with the convex border turned forward, the concave one back- 

 ward, as in Amphiuma, they form the chief part of the articu- 

 lar cavity for the humerus. It is most probable also, that as 

 in Amjohiuma, a portion of the broad coracoid remained in the 

 cartilaginous state, and that the reniform plate answers to 



* " Die kehlbrust platten konnte man der tinpaarigen Platte und dem ersten 

 Platten-paar im Bauchpanzer der Schildkroter vergleichen." ( Op. cit., p. 100.) 



