358 Mr. H. Seeley on tivo new Plesiosaurs from the Lias. 



prominent mamillate eminence, as in P. Neocomiensis. The 

 sides are flat, and margined by wide, elevated, rugose borders; 

 they meet beneath in a sharp mesial ridge. The subqua- 

 drate neural spine is rounded at the top, and from front 

 to back measures 1^- inch. The costal surface is circular. The 

 limit of the neurapophyses on the sides of the centra may be 

 clearly seen in the figure. The last cervical has the costal sur- 

 face divided by a horizontal groove. 



Then follow three pectoral vertebrae. The costal surface has 

 now become narrow, elongated, slightly elevated, and marked 

 by a depression on the centrum, immediately under it : it is 

 not so near the anterior border of the vertebra. The neural 

 spine of the last of these is a little broader and higher than in 

 the succeeding vertebrae. 



The seventh centrum is unquestionably the first dorsal. The 

 costal surface is now entirely on the neural arch, is greatly 

 elevated and enlarged, oblique, and looks backward. The 

 centrum is 1-^ inch long. There are eleven consecutive dorsal 

 vertebrae, and three more indicated by continuous ribs in situ. 

 The rib of the second dorsal is 10-L inches long ; but towards 

 the end of the series the ribs rapidly become short, and the four- 

 teenth is only 4 inches long. The tenth and eleventh (which 

 are the only centra seen) show pinched-in sides, sharp articu- 

 lar margins, and the outer part of the articular surface flat. 

 The eleventh is 1^ inch long, and about 2 inches high. 



The episternum is a large bone with broad wings which 

 taper to a sharp point behind, and between which, in front, 

 there is a deep crescentic cup. It is flat and thin, measuring 

 mesially — from middle of cup in front to end of wedge behind 

 2-^ inches ; from horn of crescentic cup to end of wedge 4^- inch ; 

 from middle of cup to end of lateral wing 34- inches. 



What remains of the coracoid conforms to the usual type ; but 

 the scapula and clavicle are remarkable. 



Two inches of the coracoid go to form, with IJ- inch of the 

 scapula, the deep glenoid cavity for the left humerus, measur- 

 ing 2i inches across. 



On its under side the scapula sends down a sharp ridge, which 

 extends all along the straight, flat, and perpendicular anterior 

 side. The side interior to the ridge is narrow, oblique, and 

 concave, and, with the coracoid, forms the pectoral foramen. 

 What is preserved of it measures 5 inches along the exterior 

 ridge. From centre of the glenoid cavity to the pectoral foramen 

 is 1\ inch. Least distance from ridge to pectoral foramen is 

 1^ inch. The pectoral foramen seems to have been elliptical, 

 2f inches long and \^ inch wide. 



But the clavicle, which does not appear to have been detected 



