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 of 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, 1 and the latter, from very imperfect material, by Packard. 

 Mr Schuchert gives a new figure of Protocaris showing a little more 

 detail, refigures the type specimens of Dipeltis, 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. 



*o' 



Protocaris marshi 



This fossil, only known in one specimen from the very oldest fos- 

 silif erous 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, pi. x. fig. 1 ; Amcr. Nat., 1885, p. 293 ; 

 Mem. Nat. Acad. Sri., Hi. pt. 2, p. 145, pi. v. 



