G. R. Wieland — On Marine Turtles. 119 



the offer to Dr. Hay of a photograph of the mounted skeleton 

 in time for use in his volume. 



The tenth ribs verify the original and excellent figure of the 

 carapace in an important detail. In that figure, these ribs are 

 both shown as distally restored to a length indicating support 

 of the last marginal, were that element present. This restora- 

 tion is correct, the right tenth rib having since been found 

 complete, so that the length of the entire series is now abso- 

 lutely known ; and it should here be emphasized that while 

 some of the ribs had disintegrated on one side or the other of 

 the carapace, there is not a pair in the succession, from the 

 first to the tenth inclusive, that lacks either a right or a left 

 member complete to the tip. 



This functional development of the tenth rib is unique in 

 the Thecophora. It denotes either a more primitive condition 

 or a restrengthening of this element in compensation for a 

 carapacial shield not only in process of reduction, but probably 

 also of replacement by an external dermal series corresponding 

 to the usual Testudinate keels or lines of longitudinal develop- 

 ment. 



The Marginals. — The marginal series of A. ischyros, type, 

 is considerably restored in the figures given (Plates II-IV), but 

 not hypothetically so. There are present in sufficiently good 

 condition for the determination of all the main features, margin- 

 als referred to ribs extending all the way from the second to 

 the eighth or ninth rib. Further, the fine third marginal is 

 present (cf. figure 5), which in Protostega (Archelon) Marshii 

 is suturally united with the fourth to sixth, the latter species 

 having marginals of quite the same form as in A. ischyros, type. 

 In the additional specimen of A. ischyros obtained in 1902, the 

 seventh (?) marginal is also present, while the first to fourth 

 are positively known in Protostega Copei (cf. figure 2). 

 Hence, remembering the functional tenth rib, it may be defi- 

 nitely stated that each rib beginning with the second bore a 

 marginal and that the pygal marginal, the only member of the 

 peripheral series not recovered in any of the larger forms 

 of the Protostegidse (it is present in P. advena), was thin, 

 short, and broad, and must have had the form shown in the 

 restoration (Plate II). 



The noteworthy and strange feature of the marginals is the 

 strong digitation of both the superior and inferior plates and 

 also of the anterior elbow formed by the outer border of the 

 third marginal. Were it not for the fact that in P. Copei the 

 junction with the second marginal is definitely shown, it would 

 scarcely be suspected that the true articulation of the third 

 marginal with the second in A. ischyros, type, takes place by 

 means of its long spinelike extension, which projects upward 



