348 Description of several new Trilobites. 



Our fragment exhibits eleven articulations of the abdomen, and 

 nine of the costal arches, all in a good state of preservation. It 

 presents another example of the fact, that the ribs of the side lobes 

 do not always correspond in number and position with the articula- 

 tions of the vertebral column. 



Like most of the fossil animals of this genus, the head is mutila- 

 ted or lost ; yet what seems to have been a small fragment of the 

 front or middle lobe of the buckler, lies on the rock at a little dis- 

 tance from the abdomen. It is marked by two deep curved, trans- 

 verse plicae or folds. 



The body is much depressed ; the middle lobe is slightly conical, 

 and terminates in a very obtuse tip ; its articulations are all regularly 

 rounded and smooth. The costal arches are also rounded, and 

 without striag, grooves, or pustulations, and have the same breadth 

 throughout ; the lower ribs are slightly curved, and they all termi- 

 nate very abruptly in the membranaceous expansion. This organi- 

 zation of the Asaph is beautifully developed in our specimen ; — the 

 membrane is narrow, even and smooth along the sides of the body, 

 forming a regular hem or border ; at the central portions of the tail, 

 it gradually widens and makes a short rounded projection. It is dif- 

 ficult to say, whether the whole caudal membrane is entirely perfect 

 in our specimen, for there appears to be an acute point in the rock, 

 formed by some animal remain, just beyond the rounded end of the 

 tail. If this be a part of the animal, then the central portion of the 

 caudal membrane is acute, and not rounded. 



I am indebted to Dr. J. Trimble, of Huntingdon County, for 

 this species. This gentleman has contributed very much to the il- 

 lustration of the geology and natural history of the interesting County 

 in which he resides, and I take pleasure in calling this species by his 

 name. It was found by him not far from his residence, in a buff- 

 colored clay slate. I have examined a fine large fragment of what 

 seemed to be our present species, in the possession of Professor 

 Oliver P. Hubbard, of Dartmouth College ; but as the membra- 

 naceous expansion, if it possessed one, is broken off all round the 

 body, we could not fully determine the question. It also occurs in 

 yellowish limestone, and was found, in company with the Calymene 

 Blumenbachii, at Juliet, in the State of Illinois. 



The AsAPHus Trimblii resembles, in some respects, the A. la- 

 ticostatus, but its depressed form, its narrow membranaceous border, 

 and the regular breadth of its costal arches, with some other pecu- 

 liarities, will on comparison, readily distinguish the two species. The 



