1893. ] Geology and Paleontology. ; 999 
prefrontal is large, placed between parietal, frontal, and maxillary, 
forming the superior border of the orbit ; the jugal is exceedingly rudi- 
mentary, only connected with the maxillary; there is in all living 
Amphisbzenians no postorbital arch. The squamosal is not free. One 
tooth on premaxillary, 6 pointed teeth on each maxillary. It is dis- 
tinguished from the modern Rhineura floridana Baird, by the more 
slender form of the skull, and may be called Rhineura hatcherii. 
2. The smaller skull measures only 10 by 53 mm. Itis at once dis- 
tinguished from all living Amphisbenians by the presence of a post- 
orbital arch, and the very peculiar prefrontal. 
The nostrils are inferior in position. The single premaxillary 
nearly touches the paired frontals behind. Premaxillary, nasals, front- 
als nearly meeting in one point. The nasals are distinct and extend to 
the border of the muzzle, over-roofing the nostrils. Prefrontal very 
small, placed between maxillary and frontal; separated from the orbit 
by a descending process of the frontal, which forms the anterior border 
of the orbit. Jugal complete forming a distinct postorbital bar; it is 
in connetion with maxillary, frontal, and parietal. Squamosal well 
developed and free. One small tooth on premaxillary and 4 on each 
maxillary. 
This form represents a new genus and a new family of the Amphis- 
beenians, which may be called HYPORHINA and HYPORHINIDAE. The 
species may be named Hyporhina antiqua—G. Baur. 
Walker Museum, The University of Chicago. 
On Symmorium, and the Position of the Cladodont 
Sharks.—In a paper recently read before the Philadelphia Academy 
I have described a shark from the Coal measures of Illinois under the 
name of Symmorium reniforme. The genus Symmorium isa Clado- 
dont which differs from Cladodus Agass. in having the axial elements 
of the pectoral fin fused with each other and with the proximal basi- 
lar elements, into a single piece. 
The specimens on which this genus is founded throw much light on 
the structure of the Cladodont pectoral fin, and through it, on the 
question of the evolution of this organ among fishes. e asis 
described is mostly well preserved, and clear as to details of structure. 
It confirms the characters ascribed by Traquair to the pectoral fin of 
a Cladodus from the Lower Carboniferous of Scotland, the only 
important difference being that in the latter the metapterygium is dis- 
!Geological Magazine, Feb. 1888, p. 82. 
67 
