398 NATURAL SCIENCE [December 
are thus claimed as relations of the modern Apus. Now, however, 
that the claims of Apus to have been co-existent with and in some way 
closely related to the Trilobites are being reasserted on the basis of 
a new interpretation cf the morphology of the former and of new 
facts as to the organisation of the latter—other mysterious relations 
are cropping up. With two of these—viz., Protocaris from the Lower 
Cambrian, and Dipeltis from the Lower Carboniferous, Mr Schuchert 
deals in the Proceedings of the U.S. National Museum (vol. xix.). 
Neither are quite new, the former having been figured and described 
by Walcott,! and the latter, from very imperfect material, by Packard. 
Mr Schuchert gives a new figure of Protocaris showing a little more 
detail, reficures the type specimens of Dzpeltis, and is fortunate 
enough to be able to describe three new and almost perfect speci- 
mens of the same, one of which represents a new species. 
Mr Schuchert has no hesitation in claiming both these as 
Apodidae, a welcome claim to any who, as above described, have 
interested themselves in placing Apus with the Trilobites at the 
root of the crustacean phylum. But inasmuch as Mr Schuchert 
only deals with these new claimants very generally, it has been sug- 
gested that a cross-examination of them from this special point of 
view would not be uninteresting. 
PROTOCARIS MARSHI 
This fossil, only known in one specimen from the very oldest fos- 
siliferous strata, speaks for itself (see fig. 1). Its large cephalic shield 
spreading backwards over the trunk segments, the extraordinary 
shortness of these segments in strong contrast with the wide anal seg- 
ment with its pair of cercopoda, and lastly, which is a new detail 
added by Mr Schuchert, the pair of circular markings suggesting 
eyes near the anterior margin of the carapace—all proclaim its close 
affinity to Apus. Indeed, on first acquaintance with this fossil, I 
went so far as to suggest that it might with advantage be called 
Apus marshi. 
Since studying Mr Schuchert’s paper, however, I have been struck 
by two features which seem to me to have been generally over- 
looked, one of which is of prime importance. A comparison of 
the abdominal segmentation of Protocaris and Apus appears to 
show that the former retained a primitive condition which has been 
secondarily lost in the latter. 
One of the principal arguments in favour of the great antiquity 
of Apus was found in the fact that a great and varying number of 
posterior segments are fixed in a rudimentary condition. The evi- 
dence for this was found in the progressively diminishing sizes of the 
1 Bull U.S. Geol. Survey, 10, 1884, p. 50, pl. x. fig. 1; Amer, Nat., 1885, p. 293 ; 
Mem. Nat. Acad. Sct., iii. pt. 2, p. 145, pl. v. 
