VEETEBEATES. 139 



occupying about half the antero-posterior diameter of the spine midway 

 between the extremities, but proportionately niucb smaller towards the 

 apex, lateral and posterior walls about the same thickness. Base or 

 inserted portion unknown. 



The form indicated above is known by a somewhat imperfect speci- 

 men, both extremities being broken away and distorted along the one 

 side of the posterior face, but which clearly exhibits the superficial 

 characters and thereby its distinguishing features as compared with 

 other forms. From previously described ichthyodorulites from American 

 formations, which have been referred to this group, it obviously differs 

 widely. Apparently intimately allied to the Coal Measure form, A. bel- 

 lulus, the crowded condition of the costre along the anterior margin on 

 either side at once affords a distinguishing feature in contrast with that 

 form. The apparent absence of intercostal tubercles renders its iden- 

 tity with the present group open to a doubt, but the arrangement of the 

 costse and the intervening spaces indicate its intimate relationship with 

 the forms referred to this genus. 



Position and locality: In the upper division of the Chester lime- 

 stone; Carroll's place, Pope county, Illinois. 



ASTEEOPTTCHITJS BELLTJLTJS, St. J. and W. 

 PI. XVI, Fig. 7. 



A fragment of a small spine from the horizon of coal No. 5, referable 

 to the above genus, is characterized by its somewhat stout proportions, 

 gradually tapering from base to apex, and very slightly curved outline 

 viewed from the side, transverse section subtriangular with curvilinear 

 lateral faces. Anterior margin forming an acute angle traversed by a 

 relatively strong, rounded enameled keel, similar to the longitudinal 

 ridges which occupy the body of the spine, from which it is separated 

 by a broad, shallow space about equal to that occupied by two of the 

 lateral ridges ; of the latter there are seven or eight iu either face, grad- 

 ually becoming smaller towards the posterior angles, in diameter about 

 equal to the intervening grooves, and rarely interrupted by faint nodes; 

 intercostal spaces delicately striato-puuctate, which extends into the 

 base as also in the posterior face, with rarely occurring, minute tubercles. 

 The posterior face is mutilated by pressure, but it is apparently gently 

 concave or laterally grooved, with obtusely angular posterolateral 

 edges, forming a thin posterior wall to the pulp cavity, which occupies 

 about half the bulk of the spine at the middle, and subovate in trans- 

 verse section. The line of insertion, as shown in this imperfect speci- 

 men, was apparently very oblique, indicating the posterior inclination 

 of the spine at an angle of about 30°. The specimen was probably at 



