Vol. 58.] PHYLLOCARIDA FROM PENNSYLVANIA. 445 
Clarke, and, as at present constituted, may also include both Tropido- 
caris and Elymocaris. 
Thus far, each discovery of additional characters for the genera 
now grouped in the Rhinocaride has resulted in strengthening 
their likenesses and eliminating their differences; and it may be 
reasonably questioned whether they are all morphologically distinct. 
The structural elements of the cephalothorax are the same, and the 
genera seem to differ chiefly in the presence or absence of carinz, 
the number of these, the character of the truncation of the posterior 
ends of the valves, and the number of exposed abdominal segments. 
It is not within the proper scope of this paper to attempt a revision of 
the generic and specific synonymy of both American and European 
forms. A brief review of the literature, in connection with the 
study of a considerable collection representing a large part of the 
Hamilton and Chemung species, leads to the conclusion that there 
are distinct groups of species to which most of the existing generic 
names may be applied. A number of characters, however, such as the 
presence of the rostrum and the median lanceolate plate, hitherto 
serving for generic distinction, must now be considered as of patro- 
nymic or subordinal value. 
Dithyrocaris has been shown by Jones & Woodward’ to have a 
median dorsal ridge, consisting of a carinate narrow plate apparently 
superimposed over the inner edges of the valves. No rostral plate 
has yet been discovered, though it is quite evident that this genus 
should be included in any discussion of the members of the family 
Rhinocaride. 
TROPIDOCARIS BICARINATA. (PI. XIX, figs. 1-5.) 
Tropidocaris bicarinata, Beecher, ‘ Ceratiocaride from the Chemung & Waverly 
Groups of Pennsylvania’ 2nd Geol. Surv. Penn. vol. PPP (1884) p. 16; Hall & 
Clarke, ‘ Palzont. of N. Y.’ vol. vii (1888) p. 184. 
The new features to be added to this species are of considerable 
interest and morphological value. First among these may be 
mentioned a small node or spot in each valve, a little behind the 
so-called optic node, from which a number of vascular lines 
extend backward radially over the surface. One line curves inward, 
meeting the hinge near the posterior end; while the others seem 
to be confined between the two principal carine, and occasionally 
are branched at their ends. A similar vascular marking has been 
observed by Clarke? in Rhinocaris columbina, var. livonensis, Clarke, 
from the salt-shaft at Livonia (N.Y.), and is also present in 
specimens collected by me from the Cayuga-Lake section. They 
show the lines originating near the hinge, a little dorsal to the optic 
node. Obviously, these vascular markings are indicative of some 
important internal organ. Their position posterior to, and outside 
of, the cephalic area, with their point of origin at or near the lineof 
attachment of the abdomen with the carapace, is precisely the same 
1 Monogr. Pal. Soc. ‘ British Palzeozoic Phyllopoda’ pt. iii (1898) p. 131. 
2 * Devon. Phyllocarida tr. New York’ [No. 3 of ‘ Notes on Palzxoz. Crustac.’ | 
N.Y. State Mus. Rep. State Pal. for 1900 (1901) App. iii, p. 100 & pl. iv, fig. 14. _ 
