200 PALEONTOLOGY OF NEW YORK. 



anterior extremity, so that in extremely small individuals the carapace is 

 very shmt and cordate in outline. These variations in outline have been 

 regarded by the Committee of the British Association on the Fossil Phyllo- 

 poda (Second and Third Kepts., he. cit.) as of specific value, but abundant 

 material leaves no doubt that the difference is developmental and not 

 specific. Specimens are not infrequently found folded symmetrically along 

 the dorsum, although there is no evidence of any dorsal suture or anchylosis 

 along that line. The substance of the test is chitinous and verv thin. 



Dimensions. The variation in size exhibited by specimens of this species 

 is considerable. The average normal adult represented by the type specimen 

 having a length of 28 mm., and a width of 16 mm. ; the smallest individual 

 observed is 2 mm. long and 3 mm. wide. A very large fragment indicates a 

 shield upwards of 80 mm. in length. 



Distribution. Widely distributed throughout the lower horizons of the Portage 

 group as originally defined (" Naples beds," Clarke), in the towns of Bristol, 

 Richmond and Naples, Ontario county ; Sparta and Son Yea, Livingston 

 county; and in the upper sandstones of the group at Naples and Canadice, 

 Ontario county ; Portageville, Wyoming county. 



DIPTEROCARIS, Clarke. 1882. 



DlPTEROCARIS PENNjE-DiEDALI. 

 PLATE XXXV, FIG. -H. 



I>'l>'<- iiue-Dcedali, Clarke. Amer. Jour. Science, Third Series, vol. xxv. p. 122. %. 1. 1883. 



■ is i" mm -DcBdali, Jones and Woodward. Geol. May.. Or,-, iii. vol. i. No. 8, p. 349. 1884. 

 Dipterocaris pennw-Dtodali, Etheridge, Woodward and Johes. Second Rept. Committee on Fossil Phyl- 



Iopoda el' (lie Palaeozoic Rocks, p. 11. 18S4. 

 Dipterocaris penna Dwdali, Etheridge, Woodward and Jones. Third Rept. Committee on Fossil Phyl- 



lopoda of tin- Palseozoic Rocks, p. 3. 1885. 



'I mi: original of this species consists of but one-half or one ala of the 



Carapace, which is wvy elongate, with the lateral margin straight, the anterior 



angle nearly ninety degrees and the posterior angle acute. The area of union 



"isthmus," Jones) is anterior, the cephalic cleft narrow, and the margin of the 



