468 PALAEONTOLOGY OF ILLINOIS. 



Ge^us BATACA:N t THUS, St. J. and W. 



Spines long, more or less gradually tapering and curved forward, 

 terminating in an obtuse or turgid apex, in transverse section subcireu- 

 lar or oval, without distinctly defined anterior angle and posterior face, 

 the lateral surfaces rounding regularly into either margin, and occupied 

 by more or less distinctly stellate tubercles arranged in longitudinal 

 rows, with faint intercostal sulci, and less regular diagonal series ; the 

 tubercles are often much produced along the concave anterior side, 

 especially on approaching the summit, where they form in some 

 instances strong, hollow hooks, bristling the swollen extremity, and 

 sometimes forming a few rows of obtusely conical tubercles in the pos- 

 terior side for a greater or less distance below the apex. Base mode- 

 rately inserted, tapered interiorly. Pulp-cavity subcentral or nearest 

 the posterior border, similar in section to that of the body of the spine, 

 and apparently concealed throughout the extent of the external body. 



Perhaps the most marked peculiarity of the spines above designated 

 consists in their symmetrically rounded transverse sectiou and absence 

 of a defined posterior face. In curvature they resemble Xy&tr acanthus 

 and Marr acanthus , with which latter their affinities would appear to be 

 most intimate, as indicated by the denticulate character of the tuber- 

 cles towards the extremity. 



As here understood the genus embraces Drepanacanthus ? stellatus, of 

 Newberry and Worthen, who have remarked its anomalous character, 

 (111. Eep. II, p. 125), and possibly the large spine descibed by Prof. 

 Agassiz from the Carboniferous limestone of Bristol, England, under 

 the name Or acanthus pustulosus, (Pois. Foss., Ill, p. 15, Tab. 2, fig. 3, 4,) 

 which presents apparently the same arrangement of the tuberculose 

 ornamentation and similarly rounded anterior and posterior borders, 

 while the thickened wall inclosing the pulp-cavity along the concave 

 side would seem to indicate the reversed or anterior curvature of the 

 spine, the base not being preserved in the original noticed by Professor 

 Agassiz. 



A small ichthyodorulite from the Carboniferous limestone of Russia, 

 described by Col. Eomanotvskt under the name Myriacanthus semi- 

 grannlatus,* may also prove to be referable to the genus here recognized. 

 The latter form is distinguished by its straight, very gradually tapering 

 outline, nearly circular transverse section, with a large central cavity, 

 and bearing externally along one side two rows of obtuse, closely 

 arranged tubercles; the base is not shown in the specimen, which is 



* Desc. quelques restes de Poissons Fossiles, trouvis daoa le calcaire carbonifere de Gouvernement 

 de Toula. Par Hennadius Konianowsky. Moscow, Imp. l'TJn. Imperiale, 1664. 



