44 DEVONIAN FAUNA. 



pointed out, Herr Novak figures a greatly enlarged portion of the test of the 

 " Bactropus " portion of his animal, and this shows transverse furrows, but they are 

 very much finer and of a character somewhat different from those of the English 

 specimen. We may therefore conclude that the two fossils belong to the same 

 group, but not to the same species. 



As no other part of the animal has been hitherto found in Britain, I have 

 thought it best to retain the name Bactropus for the present, for the sake of 

 clearness, although Aristozoe will have to be regarded as the ultimate name of the 

 genus. It certainly could not belong to Ceratiocaris, as it is proportionately 

 much too long. 



2. Genus. — Tropidocaris, Beecher, 1884. 



This genus has an ovoid bivalved cephalothorax marked with some strong 

 longitudinal ribs. Three species have been described, all from the Devonian beds 

 of North America. 



1. Tropidocaris ? sp. PI. IV, figs. 20 a, 20 b. 



A fragmentary specimen in my collection from Lummaton seems, as far as can 

 be judged, to be part of the ventral region of the right (?) valve of a species allied 

 to T. bicarinata, Beecher. 1 In our specimen the thickened curved line seems to 

 be part of the ventral edge, and the upper bounding line may be the remnant of a 

 median ridge. If, however, we regard the curved lower prominence to be a 

 portion of a median ridge, as in Mr. Beecher's fig. 4, the upper bounding line 

 would represent a portion of a straight ridge along the dorsal region. Fig. 20 b 

 shows a reticulation observable under the microscope on the right hand portion 

 of the specimen. In fig. 8 of Mr. Beecher's plate is a coarse hexagonal network 

 on an analogous specimen, which, however, he refers to the impression of some 

 other fossil. The marking in ours is very much smaller, and with somewhat 

 irregular and very delicate mesh-lines. Such an ornamentation is not uncommon 

 among some of the bivalved Entomostraca. 



Mr. Beecher's specimens are 25 mm. and 40 mm. long respectively. Our 

 fragment is almost in the proportions of his fig. 4, but it is too imperfect for the 

 comparison to be more than tentative. 



1 1884, C. E. Beecher, ' Second Geol. Surv. Pennsylvania ; Ceratiocaridae from the Upper Dev. 

 Measures in Warren Co.,' p. 16, pi. ii, figs. 3 — 5. 



