DESCRIPTION OF DALMANITES LUNATUS 481 



Above the slate, in order, is a non-fossiliferous limestone, a layer of 

 coarse sandstone, and another, but non-fossil-bearing (?), slate. 



All of the rocks of this area have been disturbed by the uplifting and 

 tilting of the strata. This has affected the condition in which the fos- 

 sils are found, many of them being badly distorted. 



In the spring of 1903 I spent considerable time in this locality, col- 

 lecting material for the museum at Dartmouth college. In this mate- 

 rial there were several excellent pygidia of the trilobite and two cephalic 

 shields, one of which was practically free from distortion. The present 

 report is based on my study of the material which I obtained at that 

 time. 



There are good reasons why the trilobite from the Littleton area 

 should not be considered identical with D. limulurus, as determined by 

 Walcott. In the first place, the greater breadth of the cephalic shield 

 in relation to its length gives it a very marked crescentic, or lunate, ap- 

 pearance. The length of the head from the cervical ring to the outer 

 edge of the marginal limb, in what appears to be the most normal speci- 

 men, is hardly one-third of the total width. Mr Schuchert has also 

 called attention to the absence of head denticulations. 



In fact, in both form and general characteristics, the head of this tri- 

 lobite resembles very closely that of D. pleuropteryx as described and 

 figured by Hall.* 



So far as I am able to discover, no determinable fragments of the 

 thorax have been found. However, many fairly preserved pygidia 

 have been collected. The pygidium is remarkable for its great breadth 

 anteriorly, in which character it differs considerably from D. limulurus, 

 and may, on the other hand, be favorably compared to the English D. 

 caudnlus.'f This likeness also extends to the character of the pygidial 

 spine, which is short and acutely triangular in both D. caudatus and in 

 the Littleton species. In general appearance these pygidia bear the 

 closest resemblance to the pygidium of a specimen of D. 'pleuropteryx, 

 named by Green from the Lower Helderberg of Schoharie, New York, 

 the difference being not in form, but in the fewer segments in the Lit- 

 tleton species, in both the middle and lateral lobes. 



The differences between this form and D. limulurus are sufficient to 

 warrant its being regarded as a new species. In fact, in the general 

 character of both cephalic shield and pygidium, it approaches much 

 nearer to D. pleuropteryx than to the Niagaran form, and I venture to 

 suggest that it be known as Dalmanites lunatus in view of the strongly 

 crescentic, or lunate, character of the head. 



*Nat. Hist, of New York, pt. vi, vol. 3. 



f Green, in his monograph on the Trilobites of North America (1832), calls attention to the simi- 

 larity between pleuropteryx and caudatus. 



