204 



PORTHEIJS AKCUATUS, Cl)])e. 



The smallest species of tlie genus, equaling Ichthyodedes ctenodon in 

 size, is repi'esented by incomplete maxillary and palatine bones, and perhaps 

 by accoiiipanying vertebrae and other pieces. Apart from its small ^ize, 

 this species may be known l)y the compressed and concave alveolar border 

 behind and below the posterior maxillary condyle, and the very small size 

 of the teeth which protrude from its subacute edge. The superior border 

 behind this above-mentioned condyle is oblique, and its anterior border an 

 acute edge. The interior face of the maxillary is convex ; the exterior 

 plane, and anteriorly dotted with radiating lines of pore-like impressions. 



This species .is less nearly related to the precediug species of Portheus 



than they are to each other. 



Measurements. 



M. 



Depth of the luasillary behind the second condyle 0. (125 



Thickness of the maxillary behind the second condyle 0. 004 



Width of the second condyle 0. 007 



Length of the articnlar segment of the palatine .- 0.010 



From the vellow chalk of the Solomon River. Kansas. Found by 

 Prof. B. F. Mudge. 



OBSERVATIONS ON THE PECTORAL AND VENTRAL SPINES OF THE GENUS 



PORTHEUS. 



As already stated, the fin-rays of this genus are readily separated into 

 their constituent halves. The su]>erior elements of the pectoral fin are 

 laminiform and concave on the side in contact with the inferior halves, 

 which they somewhat exceed in width. The inferior halves are massive, and 

 exhibit a strong superior rabbet on the posterior margin for an overlapping 

 border of the second ray. On the anterior margin is a more shallow rabbet, 

 which soon disappears, which is covered by the superior lamina. The 

 posterior rabbet also disappears at a point varying with the species. 

 The superior lamina bears the cotylus and adjacent hook, which embrace 

 the suj)erior scapular facet; the inferior half supports the facets which 

 correspond to the inferior two of the scapula. The front of the pectoral 

 spine is sharp-edged, forming a thin blade, hardened by a deposit of dense 

 bone, which is transversely roughened. The blade is the edge of the supe- 

 rior lamina, which extends beyond the equally acute border of the inferior 

 half, the latter fitting closely to the concave inferior face of the former. 

 Both faces of the spine are covei'ed with a dense layer of bone, which is 

 marked with delicate longitudinal grooves; and, when the superficial layers 

 are broken away, the deeper ones are found to be grooved in the same 



