484 PEOCEEDINGS OF THE GEOLOGICAL SOCIETY, [June 7, 



be shown attached, but remain upon the exterior slab, as is the case 

 both in Pterygotus anglicus, in the Arbroath Museum, and Stylonurus 

 Scotlcus, described herewith. 



2, STTLONrBus ScoTicTJS, spec. nov. 



Although not so large as Pterygotus anglicus, this new species is 

 perhaps the most remarkable of all the Palaeozoic Crustacea. It was 

 found in an Old Red Sandstone Quarry in Montroman Muir, near 

 the Forfar and Montrose Pike. 



It is represented by a separate carapace (the relievo side of which 

 is in Lady Kinnaird's cabinet, and the intaglio in the British Mu- 

 seum collection), and by an almost entire example which Mr. Powrie 

 has been so fortunate as to obtain. The latter is lying on a slab 

 of Old Ped Sandstone, at full length, with its dorsal aspect exposed, 

 and the five last body-segments detached entire, so as to show both 

 the ventral and dorsal surfaces. The impression of the upper surface 

 of the same on a separate slab exhibits in the most perfect manner 

 the epimeral portions of each of the last four segments, and also the 

 remarkable spatulate telson 9 inches in length. 



The entire specimen is 3 feet 4 inches in length. The margin of 

 the carapace is much injured ; but fortunately the separate carapace 

 is well nigh perfect, so that we are at no loss to ascertain its con- 

 tour. The posterior margin of the head is at its narrowest point 

 9 1 inches in breadth and about 12 at its widest central portion, 

 and (about) 8 inches in length. 



There is an oblong median ridge in the centre of the carapace, 

 terminating in a smooth rounded prominence 3 inches from the pos- 

 terior margin, and extending forward about 2 inches. On either 

 side of this central line are two smaller oblong prominences, rising 

 more in advance of the central ridge (4^ inches from the posterior 

 margin and about |ths of an inch in length), broader in front than 

 behind, and curving away from the median line, from which they are 

 distant half an inch on either side. The central ridge and lateral 

 prominences are carried forward in a Y-shaped elevation which 

 spreads out laterally as it advances ; the whole of the front and 

 antero-lateral portion being coarsely tuberculated, a single irregular , 

 row running down the median ridge. 



The eyes are situated parallel to the median ridge, and arise ex- 

 actly 1 inch on either side. 



They are almost identical in form with those of PJiacops and Asa- 

 pliv^s, being arranged in a semilunar or horseshoe shape around a 

 raised prominence. The cornea of the eye measures 22 lines, and 

 is disposed outwards and forwards, the centre being dii-ected towards 

 the latere -anterior angles. The eyes are elevated about 5 lines 

 above the surface of the carapace ; probably they may have been 

 even higher, but are somewhat compressed. 



Very minute scale-like markings are seen on the lateral and pos- 

 terior margins of the carapace and body-segments. 



The margin of the head is double around the frontal and latero- 

 anterior portion, as in S. Poivriei and ;S'. Logcini, &c. 



