1885.] Geology and Paleontology. 701 
following results of a reinvestigation of the characteristics of the 
genus: 
What we should regard as the differential characters of the 
group Syncarida, to which Acanthotelson belongs, are tke sixteen 
free segments of the body which are homonomous or of uniform 
size; the first and second, however, being soldered together and 
We should regard the Syncarida as the lowest group of Thora- 
costraca, but much nearer the Schizopoda than the Cumacea; 
they form a connecting link between the Amphipoda and Thora- 
costraca, but at the same time in their most essential characters 
are much nearer to the schizopods than the Amphipoda. The lack 
pf a carapace, even a rudimentary one, and the homonomous 
Segmentation cause them to bear a resemblance to the Edriop- 
thalmata which they would not otherwise present. 
To the Isopoda Acanthotelson presents a superficial resem- 
blance, due to the slightly vertically-compressed body and the 
homonomous segmentation. The Edriopthalmata (Arthrostraca 
of some late authors) are defined by Claus as “ Malacostraca with 
lateral sessile eyes, usually with seven, more rarely with six or 
fewer separate thoracic segments, and the same number of pairs 
of legs; without a carapace; but this does not express those dif- 
ferences in the form of the antennz the thoracic legs and abdom- 
inal appendages especially those of the end of the urosome or 
abdomen, which are characteristic of the sessile-eyed Crustacea 
as distinguished from the Thoracostraca. 
From the Isopoda in which the body is usually broad and ver- 
tically flattened, with seven free thoracic segments, while the 
abdominal legs are lamellar and closely appressed to the short 
abdomen, our Acanthotelson plainly differs in the long biflagellate 
decapod-like first antenne; in the long homonomously ringed 
abdomen and schizopodal abdominal feet and especially the schiz- 
_ opod-like telson and last pair of feet, adapted as in the shrimps 
for striking the water from above downwards. 
The Amphipoda are in general characterized by their laterally 
46 
VOL XIX.—NO. VII, 
