205 



manner. This i)ectur;il si»iiic is a formidablo weapon, measuring between 

 two and three feet in length and two inches in width in a Portheus thaumas 

 whose mandibular ramus is a foot in length. 



The ventral rays considerably resemble the pectoral but are relatively 

 weaker. The second and third are much smaller than the first, have a 

 lonsriludinal rib on the side of one of the angles, and are scarcely flattened. 

 The first is much flattened, and exhibits a sharp anterior edge, formed by 

 the projecting border of the thinner half. The capitula of all the rays are 

 strongly curved to a beak-like apex, bearing a tuberosity on the convexity in 

 the two smaller ones. They differ from those of the anterior pectoral spines 

 in the conve.xity of their articular facets, as they do not embrace the facets 

 of the femur as do the pectorals those of the scapula. Like the latter, the 

 dense superficial layer of bone is often finely striate-grooved. 



ICHTHYODECTES, Cope. 



Proceedings of the American Pbilosopbical Society, 1870, November; Hayden's Geological Survey of 



Wyoming, etc., 1871, p. 4'21. 



Teeth equal, suljcylindric, in a single row, sunk in deep alveoli. 

 Premaxillaries short. No foramina at the bases of the teeth on the inner 

 alveolar walls. Vertebrae deeply grooved laterally. 



The species of this genus are, so for as known, smaller than those 

 of the last, and, as their remains are more perishable than those, form less 

 striking objects among the fossils of Kansas. They are, nevertheless very 

 abundant, especially in species, five of which are now described. 



The general structure in detail is much like that of Portheus. The 

 maxillary l)one is not contracted distally for a supernumerary bone, as in 

 Portheus. The quadrate is similar, and the symplectic has a wide exposure 

 on its outer foce in /. amides. An entire anterior spine of the pectoral fin 

 of/, anaides is preserved, the halves partially separated (see Plate XLV, fig. 8). 

 The superior half is wider than the inferior, and projects beyond it, forming 

 the trenchant anterior border, which is roughened by a deposit of dense 

 osseous material. The inferior half is but little thicker, and has an acute 

 posterior border; its surface is delicately striate-grooved. The spine; widens 

 distally, and thins out to an oblique, irregular edge, and was doubtless con- 

 tinued as cartilage. A ventral spine accompanies the Itones of /. prognafhvs 

 and /. mu/ilde»taftts, which is of a more robust form than the above-mentioned 

 pectoral, but not so wide. 



The vertebrae are deeply longitudinally grooved, as in Portheus, with the 

 exception of a few of the anterior. 



