392 Frof. T. Rupert Jones and Dr. H. Woodicard — 



None of the earlier fossil forms of Limuloid Crustaceans liitlierto 

 figured and described (examples of two of which, Figs. 2 and 3, 

 are given on PI. XV with Hibheriia, and of which a series may 

 be studied on pl. xxxi, figs. 1-8, Pal. Soc. Mon. Merostomata, 

 part V, 1878) aid us in finding a suitable form for comparison with 

 the shield of Sihhertia, nor do the larval stages of the recent 

 Limulus greatly assist us in this direction (see op. cit., pl. xxxiii). 

 We are therefore reduced to the conclusion that Hibhertia may be 

 more conveniently placed along with and near to those forms 

 referred to the genus Cyclus than with any other group. Under 

 these circumstances we prefer to regard it as being characteristic 

 of a distinct genus, and we name it after Dr. Hibbert, with whose 

 discoveries in the Carboniferous strata at Burdiehouse it is most 

 closely associated. 



From the paper by H. Woodward, already referred to, we make 

 the following extract, to show the conclusions arrived at by the 

 •writer as to the affinities of the curious little forms included in the 

 genus Cyclus, to which family, under the name of Hibhertia, our 

 specimen from Burdiehouse must now be added. 



" The presence of antennas and biramous swimming-legs proves 

 ■undoubtedly that Cyclus was a Crustacean. The large size of the 

 former and the homogeneous nature of the rest of the appendages 

 (all biramous swimming-legs, with possibly masticatory bases), 

 taken in connection with the large, slightly-bivalved carapace, 

 suggest that it is an Entomostracan and probably one of the Phyllo- 

 poda, with a broad cephalic carapace like that possessed by Apus 

 and by Daphnia ; with large swimming second antennas like the 

 latter, and possibly with a pair of stalked eyes. Cyclus, however, 

 differs from the Cladocera in being flattened dorso-ventrally, and 

 from the lowest Crustacea in not apparently possessing any true 

 jaw-parts — the head, with the labrum and mouth, being bent 

 further back than in the living Entomostraca. These differences 

 may either indicate very lowly characters or very much specialized 

 ones. Two views suggest themselves : — 



" (1) That these animals were small, free-swimming Phyllopods, 

 ■with expanded cephalic shield, swimming second antennee, and 

 biramous limbs, the bases of which served as masticatory organs, 

 no true jaws having yet been developed ; the backward position of 

 the mouth may have been brought about in order to allow as many 

 appendages as possible to serve as jaws, as is seen in Limulus. 

 Or, possibly, the beast could attach itself, like a living Daphnia, by 

 a cement gland on the dorsal side of the head, in which case it 

 might be an advantage to have the mouth as near the freer end as 

 possible and close to the swimming-legs, which were, by their 

 movements, producing the foot-currents. 



" (2) The other view is that these animals were ecto-parasitic 

 Phyllopods, although they had not lost their power of free- 

 movement, yet had become specialized in the form of their body, 

 which is flattened ventrally and only slightly convex above, the 

 whole animal being expanded horizontally, unlike most other 



