[5 J THE OSTEOLOGY OF AMIA CALVA. 751 



Lave tbey aiiytliiug" whatever to do witli the primoidal-cnmiuin, and 

 they are even separated from the exoccipitals by coiniective tissues, 

 though they overlap these bones to some extent. The greater j)art of 

 one of these bones hips over one of the bones of the shoulder girdle, 

 which latter rests with a mesially-directed process upon the hinder 

 border of the exoccipital, while its remaining process, directed forwards, 

 is attached by a strong ligament to the intercalare. This bone (Plate 

 I, Fig. 1, aS'c.) corresponds in all respects with the suprascapular" found 

 in nearly all of the Teleostei. 



Among the Teleosteans one quite constantly linds, between the pro- 

 cesses of the suprascapula, a very superficially-situated dermal bone, 

 which was first differentiated by Stannius from the supratemporal bone, 

 which articulates laterally with the squamosal, and has been termed the 

 extrascapula. This bone usually is not very large, yet in a few cases, as 

 for example in Macrodon, it attains quite a considerable size ; it then 

 resembles in a great measure the bone as just described for Amia, and 

 it is only to be distinguished from it in that it does not meet its fellow 

 in the middle line. One will therefore hardly go astray in regarding 

 the bone in Amia, designated in Plate I, Fig. 1, as Esc, as homologous 

 with the extrascapula of the bony fishes. 



The nasal region of Aonia is covered by five small dermal bones, which 

 are separated ])osteriorly from the frontal plates by a small tra: sverse 

 strip of cutis. 



The dermal bone (Plate I, Fig. 1, Eth.), placed most anteriorly of this 

 group, has the form of an equilateral triangle, with the apex directed 

 backward, and with a somewhat spreading base. It lies more deeply 

 seated in the skin than the rest of these bones that overlie the cranium, . 

 but nevertheless it shows traces of the sculpturing that characterizes 

 them all. Posteriorly, and to either side of this unpaired osseous plate, 

 lie a couj>le of small bones (Plate I, Fig. 1, Ifa.) of which the two medial 

 ones are somewhat the larger pair. These are separated anteriorly by 

 the azygos bone, just referred to, penetrating between them 5 behind, 

 they meet each other in the median line. On either side of these dermal 

 bones lie two smaller ones (Plate I, Fig. 1, An.), of which no special notice 

 need be taken. The four bones just described, more especially the medial 

 pair, form the covering to the nasal cavity. Among the three bones 

 designated by EtJi., Wa., and An. there remains, where they come to- 

 gether anteriorly, a small opening which leads to the rhinal chamber, 

 and corresponds to the anterior nasal ajierture of Amia. The iiosterior 

 nasal opening is far removed from the anterior, being situated at the 

 posterior lateral angle of the bone designated by Na. The interpreta- 

 tion of the dermal plates just described is not difficult. 



The two posterior medial dermo-bones, holding, as they do, a position 

 in front of the frontals and above the narial depressions, correspond or 

 answer to the nasal bones of osseous fishes. There is yet another con- 



iPguprascapul^- of Qi^vierj pmolita/ of QeofitrOjy and StamUws» 



