VERTEBRATES. 325 



shaped teeth, they may have, occupied the symphysial position upon 

 the jaws. 



Representatives of the genus have been found only in the Lower 

 Carhonifeions foimatioiis, which Lave afforded the forms noticed in the 

 following' descriptions. 



Perip ..ectkodus Waebeni, St. J. and W. 



'PI. 8, Fig. 25,a,b,c. 



The form here indicated is distinguished by its robust proportions and 

 relatively large size. The basal portion is moderately expanded later- 

 ally, the beveled superior edge nearly equal to one-fourth the transverse 

 diameter of the tooth, slightly channeled, and rounded into the thick 

 inferior edge, the surfaces roughly striato-punctate ; the lateral borders 

 regularly and somewhat rapidly converge from the moderately produced, 

 obtusely rounded postero-lateral angles towards the outer extremity ; 

 the posterior face is relatively deep, nearly plane vertically, slightly 

 arched inward laterally and below, and defined from the crown above 

 by a faint shoulder, as shown in fig. 25c; the inferior surface presents 

 a deeply excavated area, bordered laterally by the downward produced 

 walls of the lateral borders, which is, however, concealed in a mature 

 specimen by the inrolled anterior extremity, as seen in fig. 25c. A 

 mature specimen exhibits at least seven transverse series of coronal 

 cusps, of which the median one is very strong, rapidly tapering to the 

 acute apex, slightly curved sigmoidally with the apex directed slightly 

 forward, slightly compressed autero-posteriorly, giving an oval trans- 

 verse section, with delicate cutting edges, and ornamented in both 

 faces by numerous, delicate vertical costse, much as in Cladodus ; the 

 lateral denticles, of which there is one on either side the great cone, 

 from which latter they are quite detached, are relatively very small 

 and similar in shape and ornamentation to the median cone ; the several 

 sets of coronal cusps rise from transversely elongated coronal bases, 

 which completely isolate the contiguous sets, but which are firmly con- 

 nected with the basal portion without any visible suture or other line 

 of demarcation. The specimen figured represents a large-sized speci- 

 men, which, but for the abrasion of the anterior portion of the crown 

 by which the cusps are more or less worn down, is quite entire. 



The collections afford above a score of examples of the above form, 

 including specimens in various stages of growth, and some abnormally 

 developed individuals worthy of particular notice. Amongst the latter, 

 it is apparent that large and mature teeth sometimes produce extra 

 cusps in the newer or posterior portion of the crown ; or, perhaps, by 



