Vol. 58.] PHYLLOCARIDA FROM PENNSYLVANIA. 447 
The three characteristic nodes are present, though as yet there are 
no vascular lines developed from the one homologized with the 
crustacean shell-gland. The largest carapace measures 35 millimetres 
in length. 
TROPIDOCARIS ALTERNATA. (PI, XIX, fig. 6.) 
Tropidocaris alternata, Beecher, ‘Ceratiocaride from the Chemung & Waverly 
Groups of Pennsylvania’ 2nd Geol. Surv. Penn. vol. PPP (1884) p. 19; Hall & 
Clarke, ‘ Paleont. of N. Y.’ vol. vii (1888) p. 186. 
When this species was originally described, but two imperfect 
valves were known, and the diagnostic features consisted mainly in 
the considerable number of strong alternating carine. A single, 
though quite perfect, left valve has since been found, which gives 
the complete outline of the valve, as well as the number of carine. 
The general proportions and outline are not unlike those in 7’. 
bicarinata, but from the ventral half of the posterior margin there 
are two sharp spiniform extensions, the dorsal one being some- 
what the larger. These spines are in line with the fourth and sixth 
carinee, as counted from the hinge. There are seven carine running 
nearly the whole length of the valve, the fifth one extending to the 
anterior apex or prora. Of these seven, three are much stronger 
than the others, and are marked by a double row of minute pits 
along their summits. In the cephalic region, there are four or 
five short interpolated carina, and,.on the anterior ventral border, 
there are two more, becoming obsolescent before reaching the 
posterior end of the valve. The number and arrangement of the 
nodes in the cephalic area are not easily made out, though, in their 
main features, they apparently agree with Tr. bicarinata. 
The specimen here described measures 34 millimetres in length 
along the dorsum, and 13 mm. in width across the middle. It has 
thus far proved to be a rare species in the sandstones of the Waverly 
‘Group at Warren (Pennsylvania), and has not been noticed else- 
where. 
ELYMOCARIS. 
In this genus, as in Tvopidocaris, the cephalothorax is now known 
to be made up of four parts—the two valves, the median lanceolate 
plate, and the rostrum. The abdomen has two exposed segments, 
and three or four others are concealed beneath the carapace. 
Type, Elymocaris siliqua, Beecher. 
Etymocaris siziqgua. (Pl. XIX, figs. 7 & 8.) 
Elymocaris siliqua, Beecher, ‘Ceratiocaride from the Chemung & Waverly 
Groups of Pennsylvania’ 2nd Geol. Surv. Penn. vol. PPP (1884) p. 13; Hall & 
Clarke, ‘ Paleont. of N. Y.’ vol. vii (1888) p. 182. 
The new material shows the detailed characters of the rostrum 
and median lanceolate plate in a very satisfactory manner. The 
rostrum projects slightly beyond the points of the valves, extends 
backward as far as the optic nodes, and is widest at about the 
posterior third of its length ; surface with two longitudinal carina, 
one on each side of the middle. The median lanceolate plate is 
