20 CALIFORA'IA ACAItK.MY oF SCIENCES 



Limbs and Ciirdles. 

 Plate VII, Fui.s. IS, il and 10; Plate V[II. 



The pectoral and pelvic arclies are both represented in the type specimen of 

 Thalatfomiirits. A])parently neither arch has been moved very far from its 

 original position with reference to the remainder of the skeleton. 



Pelvic ^ircli (I ml Posterior LI nif>. — In the pelvic regioM of the type specimen 

 there are parts of several l)ones evidently re[)resenting a portion of the pelvis and 

 probably some of the elements of a hind limb. Only two of these l)ones are 

 complete enough to permit identification. Corresponding to one of them there 

 are in tlie collections two much better specimens (1*1. vii, figs. 8 and 10) giving 

 a fair idea of its form. This element is larger than the other and differs from 

 it somewhat in form. It exhibits characters which are not particularly definite 

 and might permit its identification as either of the inferior elements of the 

 pelvic arch or possibly as the femur. It is narrowed somewhat below the })roxi- 

 nial i^^nd or head and is considerably broadened distally. The expanded anterior 

 margin of the distal end is thin and slightly decurved. The distal portion is 

 thickened, excepting in the middle of the end, and is excavated along the distal 

 border. The proximal end is also excavated. On the more strongly concave 

 side of the neck there is a small foramen in all three specimens. 



This element shows some resemblance to a femur, and when first examined 

 was thought to represent that element. It also resembles the pubis in the form 

 of both ends, in the curvature of the shaft, and in the twist of the outer margin. 

 The small foramen near the proximal end might o<'cur behind a trochanteric 

 elevation of a femur or in the pubis. If this is the femur it represents a type 

 of extremity quite different from that seen in the anterior lind), the distal end 

 being turned sharply backward and slightly U})ward. Propodial elements of 

 this kind nw not uncommon in natatory reptiles, but wiien pi'esiMit in the hind 

 lind). the fore limb is usually, though not always, of a simihir character. 



Tlie other element belonging in this region (PI. vii, tig. 0) is again of some- 

 what indefinite form. It is quite similar to the first mentioned element but is 

 smaller and shows a greater expansion of the median ])ortion, producing a 

 prominent wing. This bone might l)e either pubis or ischium but is probably 

 the latter. 



A fragment of another large element lying next the ischium may represent 

 the ilium or the femur. It is nearly straight and appears to be almost circular 

 in cross-section. 



However we may interpret the elements which have been discusser!, it is 

 evident that at least one of them must belong in the inferior poi'tion of the 



