YEETEBEATES. 447 



-Glymmatacanthus iRiSHrr, St. J. and W. 



PI. XVII, Kg. 2. 



Fin-spine attaining large size, moderately curved, transverse section 

 lenticular, (truncated posteriorly"?) Lateral faces very gradually con- 

 verging in a regular though slight convexity from the posterior to the 

 anterior margin, which latter is sharply rounded, sides covered with 

 numerous (above twenty) closely approximated rows of strong, sub- 

 conical, enameled and vertically striated tubercles, the impingement of 

 which gives rise to irregular transverse or oblique arrangement, which, 

 but for its irregularity, is more conspicuous, though not so uniform as 

 the longitudinal disposition, the tubercles being spaced by once to 

 twice their diameter, the interspaces delicately striato-puuctate verti- 

 cally, but with scarcely a trace or very faint intercostal sulcation, the 

 vertical rows increasing by implantation below; individually the tuber- 

 cles present much uniformity in shape and size, being more or less 

 circular or vertically oval, rarely transversely elongated though often 

 two or more tubercles coalesce by lateral impingement, constricted at 

 the base, and rising into a low, obtusely conical prominence, whose 

 more or less eccentric apex is generally above the middle, and delicately 

 sculptured by sharp radiating ridges. Fosterior face and base unknown. 

 Pulp cavity large, probably limited to the posterior half of the spine 

 and similar in transverse section. 



The above described form, upon which the preceding generic de- 

 scription is based, is represented by a fragment of a large spine which 

 was probably at least ten inches in length when entire, but of which 

 the part before us exhibits a section of about two inches along the ante- 

 rior border; the " posterior borders, unfortunately, are broken away, so 

 that it is impossible to determine the character of the posterior face. 

 As noticed under the preceding generic description, the affinities of the 

 spine in question are somewhat doubtfully compared, on the one hand 

 with the Asteracanthi, and on the other with Drepanacanthus. But in 

 the absence of more complete material, its nature and relationship can- 

 not be satisfactorily determined. 



The species is dedicated to Mr. Charles Irish, the discoverer of the 

 unique specimen described. 



Position and locality : In the upper beds of the Kinderhook formation ; 

 near Le Grande, Iowa. 



