470 PEOE. W. J. SOLLAS ON A NEW SPECIES OF PLESI0SACETJ8 



Table of Measurements of corresponding Parts in P. laticeps, Owen, 

 M.S., and P. Conybeari. 



P. laticeps. P. Conybeari. 



inches. inches. 



Furculum, length (a.p. dia.) 60 6'4 



Coracoid, length (maximum) 170 17 - 37t5 



breadth 80 8'0 



Pubis, length of symphysial margin (a.p. dia.) 65 5*5 



„ „ parallel to outer margin (a.p. dia.) 80 8*1 



„ „ oblique diameter from inner anterior to 



postero-exterior angle 100 9*0 



Ischium, length (max. obi. dia.) 90 10'1 



Humerus, length 13 5 14*5 



Femur, length 12-5 135 



Neck, from first cervical vertebra to anterior edge of 



furculum 580 780 



Trunk, from anterior edge of furculum to posterior 



edge of pubis 48 53*0 



Number of cervical vertebrse from first to anterior edge 



of furculum 27 38 



Length of posterior cervical vertebra 2'25 2*5 



Length of dorsal vertebra 2'-375 2'65 



The anterior end of the head is broken off and missing in P. lati- 

 ceps ; so that the cephalic indexes cannot be determined. 



The regions of its vertebral column cannot be clearly defined, 

 since the pectoral and pelvic girdles conceal to some extent the ver- 

 tebrae beneath them. There is no great difference in the length of 

 the dorsal region of the two species ; as shown in the Table, in P. 

 Conybeari it is 5 inches longer than in P. laticeps, a difference which 

 may be accounted for by supposing the furcula of the former to be 

 displaced a little forwards. 



The widest departure is seen in the neck, its length being much 

 less and the number of its vertebras much fewer in P. laticeps ; but 

 there is an artificial look about the neck of this specimen which leads 

 me to conjecture that some of the cervical vertebrae may be missing, 

 so that, if those which remain were arranged as they were first 

 found, several considerable lacunas would appear between them. 



The lengths of the centra of the cervical and dorsal vertebras 

 make a close approximation in the two species, P. laticeps in this, as 

 in several other characters being a little the smaller. The anterior 

 cervical vertebras of P. laticeps are rugose or tubercular in the same 

 fashion as those of P. Conybeari. 



Finally, both species come from the same " gisement," the Lower 

 Lias of Charmouth. 



If my conjecture with regard to the identity of the two species 

 should prove correct (and it will require a closer examination of 

 Owen's species than I have been able to give it to decide this), then 

 of course the name " laticeps " will have to be suppressed. It occurs 

 in print in the ' Geological Magazine,' vol. iv. p. 144, but without 

 accompanying diagnosis or specific description. 



One other character of P. Conybeari alone remains for comparison ; 

 and that is the relative dimensions of its vertebral centra. If we 

 find the proportion of the breadth and height of a centrum to its 



