Miscellanies. 223 
previous letter. (See this Journal, Vol. xt1v, p. 346.) It is very rare 
that we meet with this fossil entire ; my own specimen, which is some- 
what mutilated in its smaller appendages, is the only one known to me. 
To the practical geologist it will be a matter of interest to be informed 
what fragments are of most frequent occurrence. The subjoined 
figures represent such as’are most abundant in our rocks. 
Fig. 2. Fig. 3. _ Fig. 4. 
Fig. 2 is an accurate drawing of a specimen in my own cabinet, magni- 
fied six times in linear dimensions. By referring as above to fig. 1, it will 
_ be seen that it is the cheek or lateral portion of the shield. This is by 
far the most common fragment, and it is fortunately very well charac- 
terized by its pectinate form. Fig. 3, from a fragment in my own pos- 
session, magnified to the same scale, represents the tail or termination 
of the animal. The two longer processes are continuations of the last 
costal arches, while the four intermediate smaller appendages, and the 
two exterior ones, of similar size, are attached merely to the margin of _ 
the crustaceous covering, and are similar to the fringe of the cheek in 
Fig. 2. Fig. 4, from a specimen in Mr. Carley’s cabinet, is evidently 
the same as fig. 3, but with the lesser processes broken off, as at a. 
Before other parts had been examined, this last had deceived one of 
our best naturalists, who mistook it for the anterior instead of the pos- 
terior termination of a crustacean. Since I communicated to you my 
account of the entire fossil, (Vol. xtrv, p. 346,) I have discovered that 
the best specimens are covered with elegant tubercles, showing in this 
respect a close analogy to the Ceraurus pleurexanthemus of Dr. Green. 
A fragment is not unfrequently found, which if it belongs to this spe- 
cies, would indicate a central process from the posterior margin of the 
shield, running down over the middle of the body, like a Chinese cue 
of hair. My best specimen, already referred to, is broken at this 
point, and does not settle the question with regard to such a process. 
Contemporaneous fossils —Strophomena alternata, 8. semiovalis, nu- 
merous crinoidean joints, Orthis testudinaria, Cryptolithus tesselatus, 
Calymene senaria, Isotelus megistos, and numerous branched corallines, 
