90 BRITISH PALAEOZOIC PHYLLOCARIDA. 



two such rims arises from the impression of one valve marking the ventral region 

 of the other. The extremities rarely exhibit any raised margin ; and we have not 

 recognised the dorsal rim nor the hinge-marks alluded to by Salter. 



Owing to the relative solidity of the valves this fossil is not unfrequently 

 preserved in shape, even when the " plaiting " or imperfect cleavage of the 

 compressed flagstone crosses them at various angles. Hence these valves are not 

 so much altered in form in the Skiddaw Slates as the Hymenocarides are in the 

 Lingula-flags : yet occasionally, when they lie parallel with the superinduced 

 grain of the schist, their ends are frayed out or "plaited " into a mere fringe. A 

 very much crumpled specimen from near Keswick was figured by Mr. Salter in the 

 'Geologist,' vol. iv, 1861, p. 74, before he described the genus and species in 

 detail. 



Of the great number of individuals present in the Skiddaw Slates, the shape of 

 most has been more or less modified by pressure. Though Mr. Salter adopted the 

 narrow end as the anterior in his figures, we prefer to regard the broader and 

 prow-shaped end as the front. 



Taking fig. 13 (B. M. 47935) as presenting a well-preserved outhne, we regard 

 the narrow end as the posterior, vertically truncate, and very slightly sinuous ; 

 whilst the anterior end is broader (higher), with an acute angle above the medial 

 line, and passing gently into the slightly convex dorsal margin, and with a bold 

 elliptical curve into the strongly convex ventral margin. Fig. 14 (B. M. 42162), 

 though somewhat crumpled, shows these features. Fig. 11 (M. P. G. ^) has both 

 ends modified into nearly upright curves. Fig. 12 (M. P. G. ^, D^e) has the 

 anterior almost as truncate as the posterior. Fig. 15 (C. M. ^^, -^j), has the 

 anterior obliquely truncate. How far some of these modifications may be due to 

 difierences of growth and habit it is difficult to say, but certainly pressure has 

 been mainly concerned with them. 



With regard to size, some measure ToX"i% inch, or 32x12*5 mm.; roX^ 

 inch, or 29 X 10 mm. ; 1 X;r5 inch, or 25 X 12-5 mm. ; and f X f inch, or 22 X 6 mm. 



This small, pod-like, Palasozoic Phyllopod abounds in the Skiddaw Slate 

 (Lower Llandeilo or Arenig group) at many places near Keswick — as, for instance, 

 at Braithwaite Brow, where specimens are numerous on many bed-planes of the 

 hard shales or flagstones ; and Mr. Salter mentions Causey Pike and Grassmoor, 

 Cumberland (' Catal. Pal. Foss. Cambridge,' 1873, p. 21). H.Woodward mentions 

 Barff and Longside (' Catal. Brit^^Crust.,' 1877, p. 70). It has been collected by 

 Mr. J. E. Marr at the Nantlle tramway or " Wantlle railroad," Pont Seiont, near 

 Caernarvon (Upper- Arenig group) ; see ' Quart. Journ. Geol. Soc.,' xxxii, 1876, 

 p. 134. The " phyllopod crustaceans " mentioned, ibid., p. 135, and preserved in 

 the Woodwardian Museum, Cambridge, are several specimens of Caryocaris, and 



1 Somewhat like the seed of the custard-apple, but more slender in shape. 



