456 PROF. W. J. SOLLAS ON A NEW SPECIES OE PLESIOSATJRTTS 



Pectoral Arch. 



The bones of the pectoral arch are all present, though somewhat 

 displaced from their original position. They consist of the furculum, 

 coracoids, and scapulae. 



The Furculum. 



This (fig. 2) is a large bilaterally symmetrical plate of bone, convex 

 ventrally from side to side, with two long thin tapering lateral wings, 

 one on each side, directed backwards and slightly dorsally : a tri- 

 curvate anterior margin, the central curve being a large semicircular 

 excavation, which passes into a curve convex forwards on each side ; 

 and a gently curved posterior margin convex backwards, with a 

 narrow deep incision running forwards along the median line, or 

 axis of symmetry. The lateral curve of the anterior margin passes 

 insensibly into the front margin of the lateral wing ; the posterior 

 margin meets the posterior margin of the wing in a rounded 

 angle. 



Fig. 2. — Diagram of the Furculum. (Scale j.) 



If one draws a line from the central point of the curve, which we 

 have just called a " rounded angle," parallel approximately to the 

 anterior margin of the bone, we shall divide the body into two parts, 

 the anterior of which is much thicker than the posterior, being at 

 least 1 inch across ; it is of somewhat dense or close texture super- 

 ficially, but loose and open in the middle : the posterior part is very 

 thin, a mere lamella of bone. The anterior part may be distin- 

 guished as the "body" proper of the bone ; the posterior, which is 

 divided into two by its median longitudinal fissure, is a pair of 

 " lapels ; " and thus with the " wings " we have five distinct re- 

 gions present, but of true sutures I cannot find a trace ; the whole 

 appears to be a single piece of bone, though having regard to the 

 great difficulty there often is in discovering sutures which do really 

 exist in fossilized bones, I should not wish to be thought too posi- 

 tive on this point. 



The bilateral symmetry of the bone and its median longitudinal 



