46 



SOME NEW POINTS ON THE FIN ATTACHMENT 

 OF DINICHTHYS AND CLADODUS. 



Dr. William Clark. 



[abstract.] 



While reading the paper, he illustrated his views by a new restor- 

 ation of the side plates of Dinichthys, in which he placed Prof. New- 

 berry's post clavicular D near the posterior portion of the median 

 dorsal K, and partially underlying it, fitting to the transverse ridge 

 found on the ventral side of the mediani dorsal. This bone D would 

 then be none of the lateral dorsal plates. It extended downwards 

 and forwards on the side of the fish, and on a sulcus or depression on 

 its upper anterior border rested the upper posterior angle of the 

 supra-scapula B. Below this sulcus was another sulcus quite similar 

 also on the anterior border of this lateral dorsal, on v^'hich rested a 

 srnall oval shaped bone K that passed under the supra-scapula near 

 the middle of its posterior border. 



On the anterior portion of the lower end of this lateral dorsal 

 was fitted an undescribed concavo-convex bone E, about seven inches 

 in length, which terminated at its lower end in a transverse sulcus 

 with an elevated border on its lower edge. Overlying and overlap- 

 ing portions of all these bones, was another irregular triangular 

 bone G that served to bind the whole mass together by cartilagmous 

 adhesion to them at their points of overlapping. 



These bones build the side of the fish downwards to a point 

 where the pectoral fin should be attached. In looking for a bone to 

 rest on the sulcus of this undescribed bone E, it was found that one of 

 the arms of the bifurcated end of what Prof. Newberry had named tlie 

 clavicle F, fitted closely into the sulcus, while the other bifurcation 

 over-rode the plate (G) that overlaid the other bones, and that the 

 body of the bone! F) extended slightly do w wards and backwards along 

 the side of the fish. This suggested that this so-called clavicle might 

 be the bone to which the pectoral fin was attached ; on close ex- 

 amination of a number of these bones stria E could be seen, and one 

 had still adhering to it a portion of fin. These facts together with 

 the strong homology of the bone with the bone of Stethacanthus 

 with fin attached, which Prof, dewberry had pronounced a pectoral 

 fin bone, as well as the strong resemblance of both these bones to one 

 found in Cladodus with pectoral fin attached ; confirmed the belief 

 that the bone prcviouslv known as Newberry's clavicle was in 

 reality the bone to which the pectoral fin was attached. 



The following cuts and explanations will illustrate the claims 

 made. 



