1866.] YOUNG CAEBONIFEROUS GLYPTODIPTERINES. 603 



Tyneside Naturalists' Club ^^Holoptychius sauroides, a species founded 

 by Agassiz, but not described by him. Its reference to MegalicTithys 

 is equally inaccurate. The discovery of the vertebrae and scales be- 

 longing to the tooth confirms the propriety of its erection as a 

 separate genus. 



The teeth vary in size, the exserted portion being Jq to -}-J inch 

 in height ; but the smallest exhibit the characteristic form. The 

 ovoid laterally compressed base gradually contracts into a circular 

 shaft very slightly recurved, and near the apex twice bent almost at 

 right angles, so as to have a bayonet form; the tip is sharply 

 conical. The convexity of the shaft and the posterior half of the 

 lateral surfaces are longitudinally striate ; the anterior half of the 

 circumference is smooth. Hence it follows that the most anterior 

 strise are the shortest, those nearest the posterior mesial line the 

 longest. A narrow smooth band, equal in breadth to the interval 

 of any two striae, runs up the concavity ; and from this the striae 

 depart on either side at a very small angle, tending upwards and 

 forwards towards the anterior surface. Their number is increased 

 by bifurcation, or by the intercalation of new striae ; none pass on 

 to the first knee-bend of the tooth. The lateral compression may be 

 simple or proceed to form a shallow depression which does not oc- 

 cupy more of the lateral surface than one-half in breadth or height, 

 and near the base gives the transverse section a dumb-bell shape. 

 The basal plications are rather rounded undulations than the sharp 

 folds of other Ehizodonts ; they do not interfere with the striations. 



No skull has been found ; but a fragment of a mandible is pre- 

 served, whose vertical measurement, if complete, is small in propor- 

 tion to the height of the tooth. Close to the alveolar margin a patch 

 of the outer surface remains, and shows smooth tubercles connected 

 by low ridges in a reticulated pattern, like that of the jaw of Rhizodus. 

 The mode of arrangement of the teeth is very uncertain. There 

 can be no doubt, however, that difi'erent sizes occurred in the same jaw, 

 the larger projecting at intervals above the smaller, as in Rhizodus. 



A slab from the Fifeshire coal-field, lent me by Mr. John Young 

 of Glasgow, exhibits these teeth along with scales which are thin- 

 ner than, but essentially similar to, those of DendroptycJiius. They 

 are cycloidal, the anterior margin is flattened, and the posterior some- 

 what pointed. The exposed area is relatively smaller than in Den- 

 droptychius, less even than in HoloptycMus. The radiating grooves are 

 narrower, straighter, and fewer in number than in the last-described 

 genus, and very rarely, if ever, bifurcate. The concentric striae of 

 the overlapped area are faintly and equally radiated at all points. 

 The growth-lines are indistinct on the smooth under surface ; a lon- 

 gitudinally oval flattened boss projects from the centre ; and from 

 it a line frequently runs to the middle of the anterior margin, 

 against which the concentric lines on either side appear as if 

 faulted. The scales, in consequence of their delicacy, are not well 

 preserved : this description may afterwards, therefore, require cor- 

 rection ; but the main features are unmistakeable in their similarity 

 to those of Dendrojptychius. 



