62 BRITISH FOSSIL REPTILES. 



ray ; tlie medial longitudinal ray or stem does not exceed the transverse portion in extent. 

 The clavicles are powerful bones, pointed at each end, overlying the transverse rays of 

 the episternum, and continued along the anterior border of the scapulae towards or near 

 to the ' base ' or free extremity of those bones ; the joints are rough or sutural. The 

 scapulae are oblong, subconipressed, truncate at the free or basal end, thickened and 

 broadened at the opposite or articular end for the two joint-surfaces of the coracoid 

 and humerus (53) respectively. 



The two pairs of limbs (ib., fig. 1, s, p) have been found in every sufficiently preserved 

 skeleton, and where such fins have been lost their supporting arches or some elements 

 thereof have usually indicated their existence. Of these limbs the anterior or pectoral («) 

 surpass in size, but in different degrees according to the species, the posterior or pelvic (p) 

 pair. They appear to be most nearly equal in size in the skeleton, in part restored, of the 

 Ichtliyosaurus jjlatyodon (Tab. XXVII, fig. 1), but confirmatory evidence of the degree of 

 difference is desirable in regard to this species. The pelvic pair is the smallest relatively 

 in Ichtliijosaurus latimanus, Ich. communis, and Ich. breviceps, but the inferiority is 

 nearly the same in Ich. intermedins (Tab. XXVI, fig. 1). 



In all the species the digits are supported by flattened, subquadrate, hexangular, 

 pentangular, transversely quadrate, or rounded phalanges, exceeding in number in each 

 digit that known in any other Reptile, and recalling the many-jointed rays of the pectorals 

 and ventrals of Fishes. 



The shorter-snouted species have the greater number of digits, with more and smaller 

 phalanges ; as the jaws proportionately elongate the number of digits decrease, and their 

 plialanges become relatively larger and fewer. 



In all Ichthyosaurs the pectoral limb includes a humerus (see the typical restoration, 

 Tab. XXIX, fig. 1, 53), two antibrachials (54, 55), three proximal carpals (55), and four 

 distal ones (56'), from which the more numerous series of ossicles (57) are continued. I 

 shall here limit the description of this part of the skeleton to the modification presented 

 in the IcJdhyosaurus commnnis (Tab. XXIV, fig. 1, «). 



In this species the length of the humerus is but one fourth more than its breadth, 

 and this is greater at the proximal than the distal end. The joint-surface of the head of 

 the bone is subconvex, produced outwardly or anconally upon a thick deltoid ridge, 

 subsiding half w' ay down the shaft ; there the ancono-thenal compression becomes more 

 marked and is continued to the distal end, which is pretty equally divided into two sub- 

 concave, almost flattened, surfaces for ligamentous union with the antibrachials. 



Assuming the prone position of the fin, which presents to outside view its anconal 

 surface, as in Fishes, the anterior antibrachial represents the radius (54), the posterior one 

 the ulna (55). Both bones are pentagonal by reason of the truncation of their distal 

 approximated angles, which give lodgment to the proximal angle of the middle hexagonal 

 carpal bone ; the radial and ulnar carpals (56) are transversely oblong, and the quadran- 

 gular shape is but slightly disturbed by the production of their contiguous borders into the 



