G. R. Wieland — Archelon ischyros. 401 



pelvic region tlie connection between the carapace and neura. 

 spines is no more than one of contact, while in the sacral and 

 caudal regions there is no connection whatever. 



Measurements of Carapace. 



Meters. 



Total length of portion preserved (exclusive 



of nuchal and part of pygal) 1-515 



Estimated total length, exclusive of nuchal .. 1*70 



Breadth between 2od and 3rd ribs -40 



" " 5th and 6th " -40 



" " 6th and 7th " -45 



" " 7th and 8th " -36 



" " 8th and 9th " -28 



Narrowest portion of pygal anteriorly "10 



Thickness of carapace.. _. •002-'015 



Ribs. — The ribs, of which there are nine pairs, are remark- 

 able for their distal increase in thickness, only 2*5*^"' in thick- 

 ness at the edge of the carapace ; the distal two-thirds of their 

 length is very massive. In the five anterior pairs the thick- 

 ness three-fourths out, that is at 75^°" from the centra, is from 4: 

 to 5*^™. The width is quite regular, and the surfaces, for the 

 four-fifths of the length free from the carapace, is markedly 

 striate longitudinally. In cross section the ribs are T-shaped 

 as they emerge from the carapace, medially they are triangular 

 merging into flattened elliptical distally. The two anterior 

 and two posterior pairs have shallow longitudinal grooving on 

 their upper surface. 



In cross-section the ribs show, following a very thin, dense 

 outer layer of bone, a concentric lining, grading into a some- 

 what spongy interior. 



Measurement of Ribs. 



Meters. 



Length of 1st rib. "95 



" " 2nd " 1-01 



" " 3rd '' 1-02 



" " 4th " 1-02 



" *' 5th " _. 1-01 



Average thickness of above ribs as they 



emerge from carapace "025 



Thickness of third and fourth ribs half way out, '05 



Width half way out, 1, 2, 3, 4, 5, 6, 7, 8, 9, 

 respectively, -075, -075, -078, -075, -07, -065, 

 •06, -055, -05. 



Vertebral Column. — Five of the cervical centra with three 

 arches were recovered, the last three being in place. The neu- 



