GEOLOGICAL SOCIETY OF PENNSYLVANIA. 



265 



the body; the specimen, like all such occurring in slate, 

 is compressed and somewhat distorted. 



Dimensions : total length of the impression rather less 

 than five-eighths of an inch ; greatest breadth rather less 

 than six-eighths. 



Locality : Utica, state of New York. 



Geological series : carboniferous slate. 



Cabinet of the Lyceum of Nat. Hist., New York; 

 plaster casts in the Cab. of Geol. Soc. of Pennsylvania. 



A second impression of the body without the head, 

 occurs on the reverse surfaces of a schistose slab, more 

 perfect and less compressed than the body with the 

 head attached, and which is figured now for the first 

 time. Vide pi. 15, fig. 4. 



2. Paradoxides arcuatus. (H.) PI. 15, fig. 1, 2, 3. 



Several other triarthritic specimens accompanied the 

 above from the same locality; they consist of the buck- 

 lers only, and bear ?ome analogy with the " Triarthrus 

 Beckii" of Green (Vide Monograph, p. 87, fig. 6, cast 

 No. 34). The description of this species is herewith 

 transcribed, with the necessary corrections to render it 

 intelligible. Cauda [capite] subrotunda, bipunctata; 

 articulis abdominis [frontis] tribus, absque lobis laterali- 

 bus consuetis, sed lobo arcuato utrinque opposite.'' 



The P. arcuatus, however, differs from his description 

 and figure in the greater proportional size and form of 

 the lateral lobes of the buckler, which are fully half the 

 breadth of the middle lobe, ventricose, and prominently 

 arcuated on their exterior borders, narrowing above and. 

 completely surrounding the middle lobe, of which it forms 

 the anterior border : whilst these portions in the de- 

 scription of the T. Beckii, are represented by the author 

 as forming narrow cuneiform appendages to the sides.'' 

 This description does not accurately correspond with, at 

 I.— 2 I 



