32 Description of Genera and Si^ecies. 



is bounded by the serrated edge of the keel, while the doublure is folded inwards. On 

 the right side, however, the serrated edge of the keel only forms the boundary of the 

 anterior half, while the doul)lure makes up the other, the spines of the keel there 

 being shown end on and with their tips broken off as usual. Another point is well 

 illustrated in this specimen, viz., that many of the spines on the embossed part of the 

 carapace are not broken, and are seen to be directed forwards. There is a well- 

 marked V-shaped cervical fold passing inwards and backwards from near the base 

 of the antero-lateral spines to the mid-line of the back a little more than one-third of 

 the length of the carapace, measured from the base of the rostrum. The area in front 

 of the fold is raised into a median elongated gastric mound which is surmounted by 

 part of the sharp serrated ridge keel which is produced forward into the rostrum, 

 but when traced backwards, dies down ere the cervical fold is reached. The rostrum 

 is further strengthened by serrated lateral keels one on each side. Rows of strong 

 spines ari,se out of the grooves produced by the keels of the rostrum. On each side of 

 the central or gastric mound there is a depression with two dimples on its floor, beyond 

 which there arise mounds on each side surmounted by short serrated keels set 

 obliquely, so that if produced they would meet near the tip of the rostrum. They die 

 down, on the one hand, ere reaching the marginal band, so that there is no supra- 

 orbital spine, and on the other, in front of the cervical fold. The embossed areas in 

 front of the fold are irregularly studded with longer and smaller conical spines bent 

 forwards near their tips. The test along the floor of the cervical fold is almost free 

 from spines except where it merges into the lateral border. The area behind the fold 

 is divided along its whole length by a very sharp serrated ridge keel which merges 

 behind into the thickened posterior margin. On each side of this keel there are highly 

 embossed areas or panels extending to within a short distance of the serrated margins, 

 where the test is thickly studded with larger and smaller short conical spines directed 

 outwards and forwards. There is, therefore, a space near the serrated margins free 

 from spines or with only very fine ones. The sides of the ridge keel are also free 

 from spines. It may be, therefore, that the marginal bare space may represent the 

 upper edge of a lateral keel. The serrated margin may thus be the homologue of 

 one of the lateral longitudinal keels in Gnathophausia which often bears a flattened 

 spine, the " branchiostegal " spine of G. 0. Sars. If this be the case, then there is a 

 doublure in those species of Gnathophausia in which the keel bearing this spine is 

 developed, and such carapaces would fossilise similarly to those of our species. 



The sternites of the last seven segments (fig. 2) T. 2766"^, form a wide sternum, 

 narrow in front and increasing in breadth backwards, rapidly at first, and then more 



