384 Dr. A. Gunther on Sexual Differences 



tocephalus Gayi the arch is still broader, and joined with the os 

 petrosum throughout its length, so that the fossa temporalis is 

 perfectly closed behind. Such a development of the os frontale 

 posterius is not known in Tortoises. But, on the other hand, 

 the skull of Calyptocephalus approaches more closely those of 

 other frogs in having considerable portions not ossified, espe- 

 cially on the side of the brain-capsule. 



The ossified dermal covering of the temporal bridge and of the 

 ring round the lower and anterior part of the orbit is, I think, 

 homologous with the infraorbital arch in Fishes. The similarity 

 is greatest with Trigla and its allied genera, where the dermal 

 plate is likewise broad, granular, covering the cheek, but joined 

 to the opercular apparatus, whilst here it is attached to the 

 maxillary arch. 



The two next hones of these fossil Batrachians are two hind 

 legs ; they appear rather too slender to belong to Ceratophrys ; 

 and as the humeral bone, next to be described, decidedly belongs 

 to Cystignathus, there can be little uncertainty in determining 

 the genus to which they should be referred. But the crura of 

 the three large species living in South America are so much 

 like one another, and the form of these fossil bones agrees so 

 well with them, that it is impossible to determine the species, if 

 it is not allowed to refer at least the larger fossil to the same in- 

 dividual,^ part of which has been the humerus, which, we shall see, 

 belongs to Cystignathus labyrinthicus. They possess no peculiar 

 interest : the original separation into two bones (tibia and fibula) 

 is still visible externally from longitudinal grooves at the extre- 

 mities j at the upper extremity of the bone the groove is deeper 

 posteriorly, at the lower anteriorly ; at both extremities the bone 

 is broader ; the inner side is nearly straight, and has an angular 

 ridge nearly throughout its length; the outer side is more 

 rounded and curved. There is anteriorly, a little below the 

 middle of the length, a large foramen nutritium, and posteriorly 

 another, situated somewhat above the middle. The larger of the 

 bones is from the right side of a full-grown individual, and is 31'" 

 long without the condyles ; the smaller is from the left side of 

 a half- grown individual, and is 24'" long. In both, the condyles 

 at the lower extremity are lost. 



Far more interesting is the next bone, a left humerus, the three 

 lower quarters of which are preserved (PI. XV. fig. D.) ; it is distin- 

 guished by three high and sharp ridges ; one of them arises from 

 the tuberculum major, is thick and slightly channel-shaped, and 

 runs along the anterior and interior side of the bone downwards 

 to the lower third (spina tuberculi majoris) ; the two other ridges 

 are at the opposite side, and arise from the lower extremity of 

 the bone ; they are very compressed and thin, convergent, and 



