*S'. T. Barrett— Descripion of a 



The Trilobite described below is from the upper compact 

 beds of the Delthyris shale, a member of the Lower Helder- 

 berg formation, near Port Jervis, Orange County, New York. 

 The name, Dalmanites deniuta^ refers to the dentate margin of 

 the cephalic shield. The following are its characters. 



JJalmartites dentata. — Outline of head parabolic ; posterior side 

 concave, and posterior angles prolonged into mucronate, slightly 

 falcate extensions; its outer margin throughout dentate. ^"°° 



having about the same position as in D. pleuroptyx^ but nearer 

 the outer margins of the cheeks because of the less breadth of 

 the head ; number of lenses in a large specimen about 180, eight 

 ranges of them on the highest side. Pygidium triangular, 

 transversely convex ; posterior extremity prolonged into a grad- 

 ually attenuate spine, which is a continuation of the lateral 

 margin, and averages half the length of the axis. Axis sloping 

 evenly throughout, its inferior extremity nearly merged m the 

 border below. Two rows of minute spines extending the 

 entire length of the axis near its center, and scattering minute 

 spines either side over the surface of the segments. 



Fragments of what I suppose to be thoracic segments of this 

 species are common. Each terminates laterally in a slender 

 terete spine curved outward and upward at right angles to the 

 rest of the segment ; it has a deep narrow longitudinal groove 

 upon its lateral portion, which runs out backward toward the 

 spine, and a deeper transverse groove over its middle portion, 

 the part posterior to which is much larger than that anterior; 

 the surface has minute spines, and otherwise resembles that of 

 the pygidium. 



This species has a considerable vertical range, and some 

 layers of the rock are mainly made of its remains. It is asso- 

 ciated with Rensselaeria mutabilis, Homalonotus Vaniacemi, Lox- 

 onema Fitchiana, Chonetes complanata^ and other Lower Helder- 

 berg species, kindly identified for me by Professor Hall. 



The excellent photograph illustrating this paper was taken, 

 from one of the best of my specimens, by the skillful photog- 

 rapher of Port Jervis, Mr. E. P. Matterson. It is one and a 

 half times larger lineally than the specimen. The writer wiU 

 furnish those desiring it a second photographic plafe, giving a 

 view of the pygidium, eye prominence, and thoracic segment, 

 and has specimens for exchange. 



