CONTRIBUTIOXS TO PALAEONTOLOGY. 91 



DALMANIA BIFIDA ( n. s.). 



Pygidium small : width about once and a half the length, exclusive 

 of the caudal extension. Axis moderately convex, marked by 

 about nine or ten rings ( perhaps, in well-preserved specimens, 

 there may be one or two more). Lateral lobes marked by nine 

 or ten ribs, which are grooved along the middle and terminate in 

 a thickened border : on the posterior side the border is extended 

 beyond the axis a distance equal to half the length of the latter, 

 gradually narrowing, and the extremity distinctly bifid for half 

 its length. Surface granulose. 

 Geological formation and locality. In the limestone of the Upper Hel- 



derberg group at Stafford. Collected by C. A. White. 



DALMANIA BOOTHII. / ^ \f^^ > /^ 



1 



Cryphccus boothii : Green, Silliman's Am, Journal of Science, Vol.32, p. 344. 

 C. calliteles : Id. lb. p. 346. 



C. greeni : Conrad, Ann. lleport Palaeontology of New-York, 1839, p. 66. 



Asaphus halli [? ] : Id. lb. p. 104. 



The species originally described by Prof. Green are from strata of the 

 age of the Hamilton group of New- York, and the common form in our rocks 

 has usually been referred to the C calliteles. 



After examining at least one hundred specimens in various degrees of 

 perfection, some of them nearly or quite entire, others which are the sepa- 

 rated heads and pygidia, I am unable to point out any specific distinction 

 among the specimens of that form in New-York to which Professor Green 

 applied the name Cryph^us. The peculiar ornamentation, caused by the 

 extension of the ribs of the pygidium beyond the border, presents some 

 degree of variation, but is not accompanied by other characters which would 

 induce me to distinguish these varieties as species. In several nearly entire 

 tspecimens of small and medium size, I find all the characters described by 

 Green as those of C. boothii and C. calliteles. 



In the pygidia of larger specimens, the characters of C. calliteles are 

 observed. In still other specimens, I observe important features, which, if 

 the reference be correct, have been overlooked in the former descriptions. 

 In the specimens before me, the entire length is less than twice the width ; 

 the head is very nearly semicircular, exclusive of the anterior border which 

 is a little produced, and the posterior angles which are extended into wide 

 flattened spines as far as the fifth rib of the thorax. The glabella is subovate, 

 the longitudinal furrows being produced in nearly a straight diverging line 

 from the base to the outer extension of the frontal lobe. 

 18G1.] 



