VERTEBRATES. 473 



delicate scutiforrn tubercles, arranged in quite regularlongitudinal rows, 

 closely approximated laterally, and vertically spaced by once to twice 

 their diameter, though irregular and often crowded towards the base, 

 and interspersed with large, similarly shaped tubercles, which form 

 perhaps three, more or less, rows in either face, widely and irregularly 

 spaced vertically, except in the convex margin, where they are more 

 numerous and more uniform in size and disposition; the tubercles, large 

 and small, are oval in outline, with delicate arched transverse crest, the 

 acutely rounded apex directed above and generally projecting beyond 

 the base of the abrupt concave superior face, the inferior side gently 

 sloping and faintly sculptured with radiating ridges; the smaller tuber- 

 cles are generally more nearly circular or transversely oval, their sum- 

 mits adpressed, while the larger ones are longer and often produced 

 into a sharp-pointed apex. The intercostal spaces are more or less 

 clearly defined by a sharp impressed line, and the interspaces, orcostai, 

 between the tubercles are delicately striato-punctate. The concave 

 margin is set with a row of strong, laterally compressed, subtrenchant 

 tubercles or denticles small or faintly striated vertically at their expan- 

 ded bases, slightly curved or hooked downward, widely spaced, the 

 distance regularly decreasing towards the apex, a medium size specimen 

 bearing perhaps six to eight denticles. A specimen one and a half 

 inches in length has a transverse diameter near the middle of about .12 

 inch, probably as great again as the lateral diameter. 



The few specimens of the above described form which we have exam- 

 ined, though more or less imperfect in one or other respect, are singu- 

 larly persistent in their distinctive characteristics. Only one example 

 preserves the extreme apex, which presents the appearance described 

 above, while its body ornamentation is precisely like that observed in 

 other individuals. One large fine specimen obtained by Professor 

 Woethen, at St. Louis, shows the very thin, transversely expanded 

 base, so very like that of Lecracanthus unguiculus. 



Position and locality : Upper beds of the St. Louis limestone ; Alton, 

 Illinois ; St. Louis, Missouri. 



Gampsacanthtjs squamostjs, St. J. and W. 



PI. XXII, Fig. 13. 



Spines proportionately short, rapidly tapering, very slightly curved 

 backward, apex obtusely pointed or terminated in a strong, slightly 

 curved spur, basal borders expanded, transverse section elliptical, 

 ttiough usually flattened by pressure. Lateral surfaces thickly studded 

 with relatively large tubercles, arranged in more or less regular longitu- 



— fii 



