The osteology of Cromeria nilotica and Galaxias attenuatus. 59 
Description. 
The accompanying outline drawing (Fig. A) will suffice to give 
an idea of the external features of Cromeria. One character worthy 
of note is the forward extension of the caudal fin folds almost to the 
Fig. A. Outline sketch of Cromeria nilotica (BOULENGER). 3: 1. 
hinder borders of the dorsal and anal fins. Concerning the viscera 
there is little to record. As implied by its provisional position in the 
Galaxiidae it is physostomous, its air-bladder and pneumatic duct 
being of a similar type to that of Salmo and having no related Weberian 
ossicles. Owing probably to the mode of preservation nothing definite 
could be made out about the genitalia. 
In the specimen examined by me, the vertebral column has twenty 
eight precaudal, and fourteen caudal vertebrae. Each centrum is 
nearly cylindrical, so that the contained chorda is only slightly con- 
stricted. In the tail no separate vertebrae are present in the upturned 
portion of the axis, but a well developed urostyle is borne by the last 
vertebra. Fused with the centrum of this are three hypural bones 
all lying in the ventral half of the tail. Related to but not fused 
with the urostyle are three other hypural bones all lying in the dorsal 
half. Distally the urostyle bears on its upper surface an arch, through 
which the spinal cord passes into the fin to be further protected by 
the halves of a stout fin-ray. Underlying the free portion of this 
cord is a cartilage of the same length as the last hypural. This 
evidently corresponds to Ryper’s!) opisthural cartilage, which he figured 
for young Amiurus, and homologised with the hypural elements. 
The vertebral column and caudal skeleton of Galaxias differ in 
no essential respects from those of Cromeria. 
The radial or interspinous elements of the other median fins of 
Cromeria are bisegmental, there being no indication of a separate mesial 
portion. Both segments are well ossified. The dorsal fin seems to have 
undergone considerable backward translocation, for the first radial is 
1) Evolution of fins and fin rays, in: Rep. U. S. Comm. of Fish 
and Fisheries for 1884, printed 1886, p. 990. 
