riilyctoinaspis, a New Genus 0/ Coccosteida3. 231 



mences on each side in the external occipital plate near the 

 postero-lateral angle of the shield. Kunning forwards and 

 slightly outwards, it passes on to tlie marginal phite, where 

 it gives off a branch backwards and outwards to the edge of 

 the shield just behind the postero-external angle. The main 

 groove then turns forwards and slightly inwards at an obtuse 

 angle, and on passing on to the post-orbital turns on the 

 middle of that bone acutely backwards and inwards, ending 

 on or near the centre of ossification of the central plate. 

 Just at tlie point where the backward turn commences, a 

 short branch is given of(' which ends in the post-orbital angle 

 or prominence. 



Mr Whiteaves represents the main groove as again con- 

 tinued forwards at an acute angle so as to end at the front 

 of the shield near the ante-orbital prominence. Judging from 

 analogy with Coccosteus, one might expect it to do so, but 

 this continuation is not exhibited in any of the specimens 

 which I have examined. 



Associated in the same deposit with the cranial shields are 

 found various otlier isolated plates, which from their sculp- 

 ture probably belong to the same fish. Of these the only 

 one which seems to be clearly identifiable is the median 

 dorsal plate (Whiteaves, op. ciL, pi. ix., fig. 2). The plate 

 which he has figured as " left pre-ventro-lateral " (ih., fig. 3), 

 if it is so, must belong to the right side of the body, but his 

 " ventro-median (?) " cannot be referable to a median position, 

 as it is unsymmetrical. The Edinburgh Museum possesses 

 a number of such detached plates of different forms, but I am 

 certainly not prepared to speculate at present as to their 

 position on the body cuirass. One thing is at least evident, 

 namely, that if those plates really belong to Pldydamasins, 

 their difference of form from those of Coccosteus certainlv 

 gives additional emphasis to the distinctness of the genus. 

 No trace of the maxillj^ or mandibles of P. Acadicus has, so 

 far as I am aware, been yet discovered. 



PJihjctcenaspis Anglicus, sp. nov. 



A good many years ago a small lot of fossils from Here- 

 ibrdshire was purcliased from a London dealer for the Edin- 



