SKtTLL AND OTHEK BONES OF LOXOMMA ALLMANNI. 201 



The parietals are a good deal shorter, but on the whole broader, 

 than the frontals, with the posterior borders of which they arti- 

 culate. They are much broader behind than in front, and are 

 joined outside by the postfrontals and squamous bones, and be- 

 hind with the pair of bones to be next mentioned. 



The parietal foramen has been already noticed. 



The pair of bones next behind and articulating with the parie- 

 tals, and which, united on the median line, overhang the occipital 

 segment of the skull, as the parietals themselves in most Yerte- 

 brata do, correspond to the pair called " supraoccipitals" by Yon 

 Meyer in his description of Archegosaurus, in his work entitled 

 " Reptilien aus der Steinkohlen - Formation in Deutschland." 

 They are irregular squares of about three-quarters of an inch on 

 a side ; their outer borders are bounded for a short space ante- 

 riorly by the squamous, and further back by the mastoids ; be- 

 hind they articulate on each side of the median line with the 

 upper border of what appears to be the true supraoccipital, and, 

 further out, slightly with the exoccipitals. They form with the 

 mastoids the posterior border of the top of the cranium. 



These bones do not exist in the Crocodilia or in the great ma- 

 jority of fishes, though they are present not only in Loxomma 

 and Archegosaurus but also in Pteroplax ; they do not appear 

 either to form a part of the skull in any other of the Labyrin- 

 thodonts.*' Occasion will be taken to notice these bones more at 

 length under Section III. Occipital Surface. 



The mastoids, which are squares of three-quarters of an inch, 

 and form the posterior external angles of the upper middle cra- 

 nial surface, lie external to, and join with, the last noticed bones; 

 in front they abut upon the squamous bones ; externally they 

 are free, and bound the posterior part of the inner margins of the 

 fossae leading to the ears. 



At the back part of the mastoids, and close under their exter- 

 nal angle, is a somewhat obtusely pointed tooth-like process, 



* Since the writing of this paper, we have found that these bones'cxist, well marked, 

 in Anthracosaurus, as well as in Loxomma and Pteroplax, as will be seen in a descrip- 

 tion of the remains of Anthracosaurus, by Mr. Atthcy, about to appear in the "Annals 

 and Magazine of Natural History" for August, 1876. 



