Mr. H. Seeley on two new Plesiosaurs from the Lias. 355 



front ; the radius, more convex than the ulna, is contracted below. 

 It measures 2^ inches over the top, If inch in the middle. 

 If inch at bottom, and is ^\ inches long. There are 8 carpal 

 bones — 5 in the upper row, 3 in the lower row; they add 

 2f inches to the length of the limb. 



The phalanges and metacarpal bones, which are gracefully curved 

 backward, are in five rows, and measure 10^ inches. There are 

 3 bones in the first row, 6 in the second, 9 in the third, 8 in the 

 fourth, and 4 in the fifth row : they have the usual flattened 

 hour-glass form, and vary much in length, the row usually named 

 metacarpal being the longest. The metacarpal of the first digit 

 is subquadrate, and not quite an inch long ; the metacarpal of 

 the fourth digit is If inch long. The most massive metacarpal 

 is that of the fifth digit. The terminal phalange is always nar- 

 row at the distal end. 



The extreme length of the femur is Sf inches : it has a large 

 hemispherical condyle, \^ inch deep and 1^ inch wide. The 

 smallest diameter of the shaft is 1^ inch, and the diameter of 

 the distal end of the bone is 3^ inches. The anterior side is 

 longer than the posterior side, but is less deeply cupped. The 

 under surface is more rounded than the under side of the 

 humerus, and has a stronger rugose thickening below the con- 

 dyle for the psoas muscle. 



The tibia and fibula are much like the ulna and radius, ex- 

 cept that the fi,bula is more reniform. 



The fibula is 2 inches wide, 2f inch long, and 2^ inches long 

 in front. The tibia is 2f inches at top, 1^ inch in the middle 

 and If inch at the base, and 2-|- inches long. The tarsus adds 

 2^ inches to the limb. There are 5 bones — 3 large ones under 

 the fibula and 2 small ones under the tibia, two large ones 

 being in the upper row, and the others in the lower row. 



The phalanges and metatarsals are straighter than the corre- 

 sponding bones in the fore limb; they are 11 inches long. 

 There are 3 bones in the first digit, 7 in the second, 9 in the 

 third, 8 in the fourth, and 5 in the fifth. As in the wrist of the 

 fore limb, the metatarsals progressively get longer to the fourth ; 

 and, as in that limb, the fifth digit articulates with a tarsal of 

 the first row. 



The ilium is near the proximal end of the femur, 4 inches 

 long. If inch wide at the compressed spathulate end, and f of 

 an inch wide in the shaft. The proximal end is large, and has 

 two articular facets — one for the femur, the other probably with 

 the pubes. 



Midway between the limbs is a triradiate bone, shaped some- 

 what like a Greek letter v, and probably showing the upper 

 surface. It resembles the ischium, but corresponds exactly with 



24* 



