CRUSTACEA. 211 



"The cheeks are triangular, more or less produced and rather abruptly rounded 

 behind. 



"Eyes small, extending backward to the line of the basal furrow and with an eleva- 

 tion of four ranges of lenses. 



"The axis of the thorax is prominent and narrower than the lateral lobes, the 

 annulations being furnished with a node at each extremity. The lateral lobes are 

 nearly plane and horizontal toward the axis, but are abruptly bent downward a little 

 less than half their length from the axis. Each pleura is grooved, the groove extending 

 beyond the point of curvature. 



"The surface of the pygidium and thoracic segments is finely granulose, as is that 

 of the cheeks of the cephalic shield, but the portions of the latter adjacent to the gla- 

 bella, as well as the glabella itself, are raised into granulose pustules of several sizes. 



"This species is extremely close to P. logani, with which it is associated, and the 

 only character which, to my knowledge, can be relied upon to distinguish them is the 

 comparative size and number of facets in their eyes. As pointed out by Hall, the eyes 

 of P. hudsonicus are smaller and possess fewer lenses than P. logani. The occipital ring 

 of the latter species has usually a pointed pustule in the center. This character is 

 never found in P. logani, so far as my experience goes, but, on the other hand, it is vari- 

 able in P. hudsonicus, and I believe sometimes inconspicuous. Otherwise the two species 

 seem to be in perfect agreement. The character of the eyes is scarcely one in which we 

 would expect to see a sexual difference manifested, but possibly the existing difference 

 is of that character. However, apparent facts of distribution would seem to oppose 

 such an interpretation." — Girty, 1899. 



Remarks — Several parts of cephala are assigned to this species. The eyes of one 

 have an elevation of 3 ranges of lenses; those of the others an elevation of 4 ranges. 

 One exhibits a small spine at the genal angle. The surface is ornamented with granules 

 which vary from those visible only under the hand lens to those visible to the unaided 

 eye — most of the larger granules are confined to the glabella. The range in sizj of the 

 cephala represented follows: Axial length about 7 to about 10 mm., width 13.5 to 

 19 mm. The cephalon described and figured by Hall has an axial length of 13 mm. 

 and a width of 24.5 mm. 



A few portions of cephala that resemble those mentioned above can be but doubt- 

 fully referred to P. hudsonicus. 



The following is a description of a number of complete, or nearly complete, pygidia 

 that are provisionally included here; pygidium semicircular, posterior and lateral 

 slopes abrupt; axis prominent, composed of 9 or 10 rounded annulations; each lateral 

 lobe has 7 to 9 rounded ribs that are wider than intervening furrows; each rib, except 

 anterior one of each lobe, marked with narrow, shallow, longitudinal groove; surface 

 ornamented with granules of unequal size — larger ones visible to naked eye. The range 

 in size of the pygidia is: Length about 4.5 to 7 mm., width about 7 to 12 mm. 



Phacops logani Hall 



Plate 56, figures 16, 17 

 Phacops logani Hall, 1859, Pal. N. Y., vol. Ill, p. 353, pi. LXXIII, figs. 15-24 (not 24a) 



25, 1861. 

 Phacops logani Girty, 1899, U. S. Geol. Surv., 19th Ann. Rept., pt. Ill, p. 571. 

 Phacops logani Clarke, 1900, N. Y. State Mus., Mem. 3, p. 21, pi. I, figs. 1-5. 

 Phacops logani Weller, 1903, Pal. N. J., vol. Ill, p. 321, pi. XL, figs. 3, 4. 

 Phacops logani Shimer, 1905, N. Y. State Mus., Bull. 80, p. 260. 



Phacops logani Clarke, 1908, N. Y. State Mus., Mem. 9, pt. 1, pp. 103, 118, pi. 10, figs. 

 1-4, 7-9. 



Phacops logam Clarke, 1909, N. Y. State Mus., Mem. 9, pt. 2, p. 138. 

 Phacops logani Ohern, 1913, Md. Geol. Surv., L. Dev., p. 497, pi. XCI, figs. 1-4. 

 Phacops logani Dunbar, 1919, Tenn. Geol. Surv., Bull. 21, pi. 2, fig. 18. 



