LOWER HELDEKBERG ROCKS. 371 



Acidiispis liaiimtn. 



Plate LXXIX. Fig. 15 - 19. 



Genus Dicranubus : Conrad, Annual Report Palseontology of Xew-York, 1841, pa. 48, pi. f. 1. 

 Dicranurus kamatus : Conrad, Idem; Catalogue, p. 39. 



Head subrhomboidal in the central part, nearly straight or slightly 

 curving in front. Median lobe of the glabella moderately gibbous, 

 depressed and narrower in front, gently rising and slightly widening 

 posteriorly. The anterior lateral lobes are low oblong tubercles, se- 

 parated by an almost direct longitudinal furrow from the median lobe, 

 and by a direct transverse furrow from the piosterior lateral lobe, which 

 is a low round tubercle. Occipital furrow well defined behind the me- 

 dian lobe, curving a little backwards around the base of the posterior 

 lateral lobe : occipital annulation well defined, with a short tubercle 

 in the middle, and projecting behind in two long, slightly diverging, 

 recurved spines. Surface pustulose, with the intermediate spaces gra- 

 nuliferous. 



Thorax [of this species?] with the axis very abruptly elevated, serai- 

 cylindrical ; the articulations of the lateral lobes extending at right 

 angles to the axis, and thence curving gradually for a short distance, 

 when they turn abruptly backwards, extending into a long round spine. 

 Surface of articulations coarsely granulose, without distinct tubercles. 

 The central portion of the head, with the recurved spines from the occipital 



annulation, is the Dicranurus of Conrad. From the form of the glabella and surface 



characters it is clearly an Acidaspis, resembling in some degree the A. monstrosa of 



Barrande. 



The few articulations of the thorax found in a separate specimen are not positive- 

 ly known to belong to this species, but differ very strongly from the A. tuberculata ; 



and since we know of no remains of other species in this rock, they are probably 



of this one. 



Fig. 15. A small individual preserving the central portion of the head and the occipital spine. 



Fig. IC. A larger individual. Fig. 17. Profile view, showing the recurved spines. 



V ig. 18. The bifurcating occipital spine of a larger individual. 



Fig. 19. A fragment of the thorax, probably of this species. 



Geological position and locality. In the shaly limestone of the Lower Helderberg 



group : Albany and Schoharie counties. 



