318 



BULLETIN OF THE UNITED STATES FISH COMMISSION. 



Pst.T. 



borders develop a raised rim, and the planes of the surfaces, contributed by the two 

 bones superiorly on either side, look upward aiid outward, the reverse being the case, 

 o? course, beneath. The posteroexternal angles, as well as the hinder border, are 

 thickened and undulating for the articulations of the heads of the ventral fln-rays. 

 There is, also, a characteristic process developed mesially on this border, into the 

 formation of which each pelvic bone takes an equal share; above it is bifid, directed 

 upward and backward, and compressed anteroposteriorly; below it is peg-shaped and 

 directed in the same degree forward and downward. 



I fail to find any bony nodules representing the actinosts between the ventral 

 fin rays and the pelvic bones in this fish; and the rays themselves seem to be con- 

 structed upon the same plan as the pectoral ones, being retained in their positions by 

 firm ligaments and the skin. The outer one, however, on either side differs materially 

 in form, being spoon-shaped, with the concavity against the next ray on its inner side. 

 It also develops an inturned process, which curves over the next two or three rays. 

 This double arrangement seems 

 designed to strengthen the inner 

 rays and assist to keep them in 

 their position. 



These jjeitjic hones are seen only 

 in part in the accompanying figure 

 of the skeleton of M. dolomieu (plate 

 44), but this statement does not 

 apply to the remainder of the oste- 

 ology of the body and tail of this 

 bass. 



Omitting a study of the scales 

 of Micropterus, which closely re- 

 semble those of most other forms 

 of the higher teleostean fishes, we 

 have still to briefly consider the 

 skeleton of the body and the skele- 

 ton of the tail. 



Counting the one from which 

 the urostyle springs, Micropterus seems invariably to have thirty vertebrw in its spinal 

 column. When I make this statement I am aware of the fact that in my paper on 

 Amia calva thirty-two was the number reckoned, but after carefully recounting these 

 on two perfect skeletons now before me, representing both species of the genus, 1 am 

 satisfied that there are but thirty of these bones. Fifteen of these vertebrae belong 

 to the abdominal portion of the column, and each one supports a pair of ribs, all of 

 which in their turn, sav§ tYkel&st five pair, have epipleural appendages. The atlautal 

 pair articulate with the vertebra at the very base of the neural arch, but as we pro- 

 ceed backward they gradually recede from this position so as to finally spring from 

 beneath the transverse processes on the under side of the vertebra. This condition is 

 characteristic of a great many of the osseous fishes. The neural and hsemal arches of 

 this form are completely anchylosed with the vertebral elements, and in the best- 

 developed segments, both superior and inferior, post- and pre-zygapophyses are 

 present. 



Fig. 7. — Sket<ih of the inner aspect of left half of shoulder girdle and 

 pectoral limh of Jf. saZmoirf^s. Pfi(. 3'., posttemporal; P5(o. T., 

 posterotemporal ; S^^/^. c.,hypercoracoid; Myo.c, hypocoracoid ; 

 P.Sc, proscapularj T., teleotemporal; T'., lower teleotemporal; 

 Ast., actinosts; P/., pectoral fin. 



