VEETEBBATES. 4G9 



about .1 inch in diameter, and probably above one inch and a half in 

 length. 



The species thus far determined belong to the Lower Carboniferous 

 formations, and that described under the specific term B. baculiformis 

 is regarded as the typical representative of the genus. 



Batacanthits baculiformis, St. J. and W. 



PI. XXI, Fig. 4, 5, 6, 7, 8. 



Spines of medium size, gently curved and very gradually tapering 

 from the base toward the turgid, bluntly terminated summit, trans- 

 verse section oval, slightly compressed posteriorly, and uniformly 

 rounded along both margins. External surface occupied by ten to thir- 

 teen, more or less, faint longitudinal costse in either side, separated by 

 a narrow sulcus, and bearing numerous radiately sculptured tubercles, 

 arranged in more or less regular oblique series gently descending from 

 the anterior to the posterior border, though subject to considerable 

 variation in the latter respect, especially in the posterior region, where 

 the transverse arrangement is very irregular. The tubercles iu the 

 anterior portion of the spine, where their apices have been more or less 

 abraded, are obliquely transverse or crescentiform, the concave side 

 toward the apex, and vertically spaced by three times their own diame- 

 ter; posteriorly they become slightly elongated vertically, and more 

 acuminate, smaller and more crowded, their eccentric apices, as in the 

 anterior rows, generally directed above. Towards the summit the tuber- 

 cles suddenly develop into strong, conical processes, which are appa- 

 rently smooth, and which form a singular bristling armature of the 

 turgid extremity, occupying the greater part of the lateral surfaces and 

 the anterior margin. Base, as shown in a fragment of a small spine, 

 inserted at an angle of about 40° with the dorsal line, strong and taper- 

 ing to an obtuse point, excavated posteriorly. Pulp-cavity nearly half 

 the diameter of the spine, lateral walls nearly the same thickness as 

 the posterior, and about half the strength of the wall along the concave 

 anterior border, extending quite to the summit, and probably opening 

 posteriorly below the line of insertion. A specimen half an inch in 

 greatest diameter near the base probably attained seven or eight inches 

 in length, about the dimensions of the largest examples at present 

 known. 



The fragments of spines of the present species are readily recogniza- 

 ble by the transverse and generally obliquely arranged tubercles of the 

 anterior region, their posterior half being generally distorted by the 

 yielding of the thin walls inclosing the pulp cavity to external pressure. 

 A beautiful example which we owe to Mr. Wachsmuth, showing nearly 



