446 PROF. C. E. BEECHER ON PALZXOZOIC | Aug, 1902, 
as that of the shell-gland or renal organ of Apus. It seems safe to 
offer this suggested homology, since it invests an external character 
with some definite physiological meaning, instead of allowing it to 
stand as a fortuitous feature of little or no significance. 
In this connection, an enquiry may be made as to the nature of the 
so-called optic nodes. It maybe stated that they are most strongly 
developed in members of the family Rhinocarids, and are well shown 
in the species under discussion. Their position is at the posterior 
end of the short carina lying anteriorly between the two great carine. 
The summit of the node has a minute pit, called the optic pit. 
No positive information is as yet attainable as to whether or not 
these nodes are real visualorgans. It is the most natural conclusion 
to reach, but, as the living Nebalia (which is analogous In many 
points of structure with these fossil rostrate forms) possesses inde- 
pendent stalked eyes in front of the first pair of antenne, it is possible 
that another interpretation should be given. As a mere postulate, 
I would suggest that they are infolded points of the test to form 
muscular fulera or apodemes for attachment of the muscles moving 
the mandibles, 
Besides the two nodes already discussed, there is still a third and 
much larger one lying outside the shell-gland, and bisected by the 
large submedian carina of each valve. I can suggest no obvious 
homology for this lobe, although it doubtless corresponds with some 
large organ or ventral appendage. 
As already noted, Hall & Clarke’ proved the existence of the 
rostrum in this species. It is a narrow lancet-shaped plate, 
with a strong carina along the middle. The presence of a median 
lanceolate plate is now determined, as shown in Pl. XIX, fig. 5 
It extends from as far forward as the optic nodes to the posterior 
end of the hinge, and is widest across the anterior fourth. Like 
the rostrum, it is marked by a strong longitudinal carina, and has 
a chevroned ornamentation, with the lines pointing backward. 
The only specimen yet found that preserves the abdomen in con- 
nection with the carapace is represented in Pl. XIX, fig. 3. In this 
example, only a part of the ultimate abdominal segment is exposed, 
together with the telson and cercopods. Detached abdominal portions 
have been found, showing two segments in front of the telson, and 
this probably represents the number capable of extension beyond the 
carapace, the others being unprotected by a strong chitinous test. 
The ultimate segment is about twice as long as the one in front, and 
is marked by a chevron-pattern, as shown in Pl. XIX, figs. 1 & 2. 
On the dorsal side, the direction of the lines is forward; while, on 
the ventral side, they point backward, and are considerably finer and 
more numerous, 
The youngest examples possess valves measuring about 6 milli- 
metres in length. They are proportionately wider than in fully adult 
individuals, but clearly preserve their specific features. The surface 
of the valves is covered with fine, wavy, discontinuous, raised lines. 
2 ¢ Palxont. of N. Y.’ vol. vii (1888) p 184. 
