290 General Notes. [March, 
about the lateral anterior border, and in the intercalated small 
plates which surround the anus between the first and second 
distinct from the marginals, as in Chelyosoma. But they are dif- 
ferently arranged in the Pterichthyidæ, one forming a median 
valve of the mouth or zotosome, and one being embraced in a larger 
posterior one. 
The following hypothesis may be framed to account for these 
further forwards than in that genus. Possibly also in this stage the 
belly will be found to be shielded like the back, which would be 
Fig. I, Fig. 2. 
‘olepis canadensis Whiteaves, from above, half size of a small 
specimen. The valve of the dorsal mouth, or notosome, is broken. (AR rg 
Chelyosoma maclovianum Brod. & Sow., $ natural size, from Point Barrow, Alaska, 
a still further point of approximation to Pterichthys. From such 
a type I strongly suspect the latter genus to have descended. 
The principal change which it has undergone has been the sub- 
stitution of the dorsal anus by the normal vertebrate position at 
the posterior extremity of the body. The tail has been retained 
European form. 
y 
- -~ represent the primitive mouth and cesophagus, as held by Geof- 
