Contributions to Fossil Crustacea. 391 



cresceutic area, except where the edge fails in for a little space just on 

 the centre of the front border; where the buckler becomes slightly 

 depressed and the narrow groove along the margin is interrupted or 

 perhaps injured there is an obscure impression of what may have 

 been a jointed antennary organ in front. The surface of the two 

 lateral areas of the buckler have a finely granulated ornamenta- 

 tion, which is most marked just within the peripheral rim of the 

 carapace, and is limited by two thin parallel granulated ridges, each 

 starting from the incurved posterior angles of the shield, the longest 

 being 7 niin. and the shortest only 4 mm. in length ; the intervening 

 space of 5 mm. in breadth, forming the centre of the carapace, is 

 devoid of the granulated ornament seen on the other parts of the 

 shield, and has only a small spine-like impression 3 mm. long, which 

 extends for three-quarters oF the entire length of the shield as 

 a curved irregular incised line. There are some other markings, 

 too obscure for interpretation; also a slight posterior projection on 

 the central line, as if possibly representing a part of a lost series of 

 caudal segments (?). 



The presence of the two corresponding angles, and the narrow 

 posterior opening between them, suggests affinities with Dithyrocaris 

 (cf. D. Scouleri as represented by McCoy, with its two raised 

 lateral ridges), but in most of the members of this group the lateral 

 portions of the shield are less circular in outline, and in many 

 the surface ornamentation is composed of linear or reticulate, and 

 only occasionally of granulate markings. Compared with the 

 shield of Apus or Lepidm-us,^ the general outline is much alike, but 

 the granulated mesolateral ridges continued forward from each of 

 the posterior angles in Hibbertia are not present in Apus, whereas 

 the median ridge so conspicuous in both Apus and Dithyrocaris 

 is apparently quite absent in Hibbertia, or is not preserved in the 

 fossil. Contrasted with the anterior (cephalic) buckler in Limulus, 

 the shield of Hibbertia is seen to be nearly circular, whilst that 

 of Limulus is semicircular ; the posterior angles of the shield of 

 Hibbertia are contracted together and directed somewhat inwards 

 at their extremities, whilst in Limulus they are wide apart and 

 directed rather outwards. The mesolateral (ocular) ridges are 

 present both in Hibbertia and Limulus, but in Limulus they form 

 a curved line, not a straight ridge as in Hibbertia. 



The granulation on the lateral areas of the shield and on the 

 ridges is also strange to Apus, and more closely resembles that seen 

 in some species of the Carboniferous genus Cycliis (cf. Cyclus 

 Johnsoni, H. Woodw.,- and C. testuclo, Peach, the former from 

 the Coal-measures of Coseley, near Dudley, the latter from the 

 Carboniferous shales — so rich in Crustacea, Arachnida, etc. — of 

 Eskdale on the Scottish borders).^ 



1 See Plate XV, Fig. 1, copied from Dr. A. S. Packard's figure. (Men. 

 Phyllopod Crustacea of North America, 1883, pi. xvi, fig. 1.) 



■■* See "Contributions to our Knowledge of the Genus Cyclus horn the Carboni- 

 ferous Formation of various British Localities," by H. Woodward: Geol. Mag., 

 Dec. IV, Vol. I (1894), pp. 530-9, PL XV. 

 ■ 3 Trans. Roy. Soc. Edinburgh, yoI. xxx (1883), p. 227, pi. xxviii, figs. 2-9d. 



