12 PROCEEDINGS OF THE ACADEMY OF 



" Descriptions of Fossils collected during the U. S. Geol. Survey 

 under the charge of Clarence King." By F. B. Meek. 



Prof. Leidy exhibited specimens of ichthyodorulites, upon which be made 

 the following remarks : 



Xiphactinus audax. The genus and species are founded on an interesting 

 specimen belonging to the collection of the Smithsonian Institution, and ob- 

 tained from the cretaceous formation of Kansas by Dr. Sternberg. From the 

 want of symmetry in the base of the specimen, I suppose it to have been the 

 pectoral spiue of some huge siluroid fish. 



It is a broad sabre-shaped weapon, in its present condition sixteen inches 

 long, which is near its original length, if one may judge from the thinness and 

 rounding of the border at the broken end. At its middle it is nearly two inches 

 broad and almost seven and a half lines thick. It slightly narrows and be- 

 comes thinner towards the outer end, and becomes thicker and more narrow 

 approaching the base. An inch and a half from the latter it is thirteen and a 

 half lines thick and seventeen lines wide; and the same distance from the 

 outer end it is the fourth of an inch thick and twenty lines wide. The anterior 

 convex border is rounded at first, but becomes subacute at its outer part. The 

 posterior concave border is rather more obtuse. 



A large groove commences back ot the root, extending outwardly, becoming 

 contracted and deeper, and opening to its bottom along the under part of the 

 spine to its outer extremity. The bottom of the groove is irregularly pitted, and 

 its upper surface formed by the overhanging posterior portion of the spine is 

 transversely corrugated or striated. A similar but shallower groove com- 

 mences in front of the root, and extending outwardly opens beneath the spine 

 at the anterior half of its surface. 



The upper surface of the spine is nearly flat and longitudinally striated, ex- 

 cept at the outer part of the anterior border, where the striation is finer and 

 curves forward. 



The root of the spine turns up into a sort of hook- like process, broken at 

 the end. It has been about two and a half inches in height from a level with 

 the inferior surface of the spine. The inner part of the root forms a vertical 

 oblong convexity, the lower half of which is occupied by a raised facet, appa- 

 rently an articular surface, upon which the spine moved. 



Prof. Agassiz, in his Poissons Fossiles, has described specimens of ichthyo- 

 dorulites from the chalk of Lewes, England, which he referred to placoid fishes 

 of the genus Ptychodus, " from the circumstance of their constant occurrence 

 in the same localities " as teeth upon which the genus was first established. 

 These rays are especially remarkable for their segmented character. " Instead 

 of being composed of a single piece, as in other genera, they consist of flat 

 rods, or rather broad, thick plates intimately united, but rendered distinct on 

 the surface of the ray by longitudinal grooves." Without question as to the 

 reference of these rays, I exhibit several similar specimens from the cretaceous 

 formation of Kansas, submitted to my examination by the Smithsonian Insti- 

 tution. The same collection of fossils, of which the rays were part, also con- 

 tained many teeth of Ptychodus Morloni, but I am uninformed whether they 

 were found in association. 



The specimens are probably two fragments of the same ray, but an interme- 

 diate piece is wanting, and they are imperfect at the opposite ends. They also 

 appear to be somewhat compressed from pressure. As a whole the ray is flat 

 at the sides, with a thickened, convex, posterior border, and an acute dentated 

 or festooned anterior border. The dentate processes are composed of a denser 

 tissue than the rest of the ray, and are thickened in a line from the point to 

 the base. The body of the ray is composed of longitudinally oblique bars as- 

 cending from the posterior border to the bases of the dentate processes in 

 which they are merged. The longer and broader fragment is four and three- 



[March, 



