398 



University of California. 



[Vol. 3. 



dosageceras, and Geltites. The Pseudosageceras seems to be 

 the only species common to these heels and those of the Aspen 

 ridge." 



On splitting the slab containing the specimen, the spine broke 

 from the surrounding matrix leaving on the rock, the thin 

 surface layer of the spine, together with the ganoine-coated 

 tubercles which ornamented it. Consequently the ornamentation 

 of the spine by tubercles was not at first evident. As tubercles 

 were supposed to exist, the surface was carefully etched with 

 hydrochloric acid and thus the whole pattern was brought out 

 clearly. Numerous individual tubercles were then extracted and 

 examined under the microscope. 



The figure of the spine (PI. 47, Fig. 1) was based on a study 

 of the complete tubercular pattern which was exhibited after the 

 etching had exposed all of the tubercles present . The arrange- 

 ment and ornamentation of the tubercles are given exactly as 

 they occur on the specimen. 



Three transverse fractures of the spine permitted a study of 

 the cross sections and furnished evidence of the character and 

 extent of the medullary cavity (PI. 47, Figs, la, lb, lc) . The 

 exact character of the deep posterior furrow at the base was 

 brought out clearly by careful removal of the limestone matrix 

 which filled it, (Fig. Id). 



DESCRIPTION. 



Cosmacanthus elegans n. sp. 



Plate 47. 



Type specimen No. M9087 University of California, Palaeontological 

 Museum. 



Spine of medium size, 163 mm. long by 23 mm. greatest width, bilater- 

 ally symmetrical, tapering, slightly arched, curving backward, cross-section 

 triangular with a sub-acute anterior angle; anterior edge covered above the 

 base by a rounded enamel ridge. The oblique dorsal line separates a smooth 

 base from the ornamented exserted portion and indicates a posterior inclina- 

 tion of about 45°. The lateral faces are slightly rounded. The posterior 

 face is truncated and hollowed below by a deep furrow which is an extension 

 of the medullary cavity. Upper portion of posterior face longitudinally- 

 elevated in a low, rounded, median ridge, or keel, between which and the 

 edges of the face are shallow longitudinal furrows. The lateral and posterior 

 faces are covered with small, closely set, and distinctly sculptured tubercles. 

 The sculpturing of the tubercles is in the form of minute oblique lateral 

 ridges which are generally longer on one side of the tubercle, thus making 

 the pattern somewhat asymmetric; the obliquity of the ridges often approx- 

 imates a spiral type. The sides of the tubercles curve sharply into a 



