DITHYROCARIS VENOSA. 



189 



Eachuba tenosa, E., W., and J., 1888. Eep. Brit. Assoc, for 1887, p. G3. 



— — Packard, 1889. Proc. Bo.ston Soc. N. H.,i vol. xxiv, p. 212. 



— — Miller, 1889. N.-Amer. Geol. Pal., p. 556. 



— — Voffdes, 1893. Bibliogr. Pal. Crust., p. 405. 



At page 299 of bis memoir on this interesting fossil, the author writes : 



" Impression of a dorsal shield in the same uodule . . . showed that it possessed a carapace 

 resembling that of Bithijrocaris in general form. It was broadly rounded in front, and its periphery 

 had a broad flat margin, which was covered, at least laterally, with very frequent, delicate, but 

 distinct, slightly incurved, uniform ridges, nearly parallel to the longitudinal axis of the body, and to 

 one another. The specimen is too [much] broken to show anything of the eyes or of any other 

 feature excepting two low longitudinal ridges marked by a sharp carina, slightly curved, opening 

 inward, one in the middle of eitlier lateral half of the body." 



The measurements appear to be as follow in comparison with those ot'M'Coy's 

 B. Scouleri (PL XXV, fig. 6 a), and the caudal extremity in PL XXI, fig. 10 : 



M'Coy's 

 D. Scoitlei'i. 



35 



D. testndhieay 

 PI. XXI, fig. 10. 



Rhachura venosa. 



Breadth of carapace, 50 mm. . 

 Breadth of its margin 5'5 mm. 

 Greatest distance of lateral ridge from the inner edge of the margin 



on one side, 10 mm. ; on the other, S'5 mm. . 

 Length of abdominal fragments and appendages (two), 48 

 Length of antepenultimate segment, 7 mm. 

 Breadth of antepenultimate segment, 9'5 mm. 

 Length of penultimate segment, 13 mm. 

 Breadth of the same posteriorly, 8'75 mm. 

 Probable length of the last segment, 5 [13 ?] mm. 

 Length of caudal appendage [style], 26 mm. 

 Breadth of the same at the base, 3 mm. 

 Breadtli of the same in the middle, 25 ram. 

 Breadth of the same at the broken tip, 1-2 mm. . 

 Length of the other appendage [stylet], broken and displaced, 26 ? mm 



The illustration (pi. ix, fig. 3, nat. size, and fig. 3 a magnified) accompauying 

 Mr. Scudder's descriptive memoir represents the ventral aspect of two broken 

 abdominal segments, and two caudal spines (a style apparently and a broken 

 stylet, both sulcate). The shield or carapace is not illustrated. From the com- 

 parison of the measurements tabulated above, this specimen appears to belong to 

 a distinct species, but of its generic status we cannot offer an opinion, except that 

 it is probably a Dlthi/rocaris. At page 297, Mr. Scudder states that the lines of 

 ornament on the dorsal surface of the abdominal joints of Bhachura are ordinary 

 raised ridges; or, if in reverse, they appear as impressed lines or furrows which 



' Dr. A. S. Packard has here given some notes on two specimens of this Phyllocaridan obtained 

 by Dr. E. R. Gurley from the Middle Coal-measures of Danville, Illinois. The fragments of the 

 carapace indicate that it was "of a general oval-triangular shape," and "a little over three inches 

 long." Two bayonet-like spines attached to the terminal segment are 15 mm. long. 



