960 MR. JJ. M. S. WATSON ON A 



less morlified, and the following list shows the direction of ch.inge 

 in passing to Batrachideiyeton : — 



1. Increase in the relative size of the " cornna " involving 



larger squamosals, postparietals, and tabulares. 



2. More anterior position of the orbits. 



3. Great decrease in size of the nasals, 



4. Broadening of the clavicles and interclavicle. 



The most interesting comparison, however, is Avith Diplo- 

 ccmlios, a type which Jeekel has already brought into relation 

 to Ceraterpeton. 



Comparison of text-fig. 162 (p. 950), the dorsal surface of the 

 skull of Batrachide)yeton, with the figures of the skull of 

 Diplocaulus given by Williston & Case, shows a A^ery striking 

 resemblance, particularly in the way in which the horn is 

 developed, by enlargement of the squamosal (prosquamosal of 

 Williston ife Case), tabulares, and postparietals (supra-occipital 

 plate of Williston & Case). 



If the bone regarded by Williston as a nasal is compared with 

 the undoubted lachrymal of Batrachiderpeton no doubt of its 

 identity can arise, it being evident that the nasals, extremely 

 small in Batrachiderpeton, axe quite lost in Diplocaidus. 



It also seems extremely probable that the bone called 

 squamosal by Williston & Case is really the postorbital dragged 

 out from the border of the orbit by the development of the 

 horn. 



The only other important difference shown on the top of the 

 skull lies in the fact that in the earlier type the frontal is, 

 excluded from the orbit, whereas in the American form it forms 

 much of the border of that opening. This depends on the 

 difi'erent position of the orbits, which in Batrachiderpeton are 

 laterally directed, whilst in Diplocaulus they look directly 

 upwards. It is in eveiy way probable that this difference 

 depends entirely on the habits of the animals in question. 



The skull of Batrachiderpeton shows no grooves for lateral line 

 organs, and it seems likely that the animal was not very 

 aquatic ; and as its skull was probably of only moderate size, it 

 is possible that it pursued an ordinary life. 



Case, apparently justly, regards Diplocaidiis as living in the 

 mud at the bottom of ponds, and its head is so enormous 

 that it must have been carried flat on the ground. Such a habit 

 of life is inconsistent wifch laterally placed eyes, which would 

 therefore necessarily migrate to the dorsal surface as in all flat- 

 bodied bottom-dwelling fishes, e. g., Lophius, liaia, Solea. 



The clavicular apparatus of Diplocauhis is very similar to that 

 of Batrachiderpeton. The clavicles in both types consist of a flat 

 ventral plate, from the upper surface of which a cylindrical 

 process rises dorsally within the lateral edge. 



The vertebral column of Dijilocrmlus is now well known. The 



