84r FIFTEENTH REPORT ON THE CABINET OP NAT. HISTORY. 



DALMANIA ANCHIOPS, var. ARMATA. 



Among the specimens in the State Collection from Schoharie, there is a 

 portion of the head of a Trilobite resembling the Dalmaiiia anchiops. The 

 diameter across the base has been fully three inches : the occipital ring 

 bears a strong rounded spine, which has been an inch and a quarter long ; 

 and the transverse diameter, at its junction with the annulation, is half an 

 inch. 



In a well-marked head of D. anchiops, more than two inches in diameter, 

 the occipital spine is less than a quarter of an inch. 



For the present, I propose to indicate the form with the strong spine as 

 a variety, D. armata. 



Geological formation and locality. In the Schoharie grit : Schoharie. 



DALMANIA SELENURUS. 



Asaplius selenurus : Eaton, Geol. Textbook, 1832, 



Calymene? odontocephala : Green, Supp. to Monograph, etc. p. 9. 



Odontocephalus selenurus : Conrad, Aun. Rep. Falseontology N.York, 1840, p. 204. 



— — : Vanuxem, Geol. Report Third District New-Y'ork, 1842, 



pp. 139 & 140, f. 1. 



— — ; Hall, Geol. Rep. Fourth District New-York, 1843. 



jyalmania selenurus : Hall, Corrected List of Fossils, Twelfth Annual Report of 



Regents on the State Cabinet, p. 88. 



This species, originally described by Prof. Eaton from a specimen of the 

 caudal shield, is regarded as a characteristic species of the Corniferous lime- 

 stone of the Helderberg mountains. The caudal extremity is produced into 

 two short spines, leaving the posterior margin crescentiform, whence its name. 

 At the time of t"he original description of the species, the head had not been 

 determined. Dr. Green, however, obtained a separate head, which he de- 

 scribed under the name of Calymene odontocephala. Subsequently, in 1840, 

 Mr. Conrad saw an entire specimen from Auburn, showing that the head 

 and tail, which had been referred to different genera and species, were in 

 reality parts of the same trilobite. Since that period, several entire specimens 

 have been obtained, and the species is supposed to be well known. 



In the examination of the specimens usually referred to D. selenurus^ I 

 find some characters incompatible with a single species. 



The original description was founded on specimens of the caudal shield 

 obtained in the Helderberg mountains and at Schoharie ; and in examining 

 authentic specimens, I find the anterior border of individuals from these 

 localities to be margined by ten toothlike processes forming a fimbriated or 

 denticulated edge, from which the name Odontocephalus was suggested. 

 These apparent denticulations are produced by oval indentations or per- 

 forations through a wide frontal border ; and though they appear separated, 



[ Septexabar, 



