204 BRITISH PALEOZOIC PHYLLOCARIDA. 



John Smith, of Kilwinning, two counterparts 1 of a dithyrocaridal valve, which 

 has a remarkable similitude in some respects to L. senigmatica. 



1. Fig. 14 represents a nearly perfect right-hand valve in its lateral aspect. It 

 is 75 mm. long by 15 mm. broad, of a pod-like shape, 2 nearly straight dorsally, and 

 shallow-elliptical on its ventral margin. This is most convex in the middle, and 

 narrows more obliquely at the compressed anterior extremity ; the edge, however, 

 is broken away at both ends. The middle third of the ventral border is markedly 

 smooth, being probably a flange, turned in and pressed flat. A delicate rugose 

 ridge lies along and within the middle part of the ventral edge, with a rather less 

 curvature, and with its ends running into that border at about a fourth of the 

 length of the valve from each of its extremities. 



The dorsal edge is neatly bent along its length into a narrow fold (Fig. 16 b), 

 which possibly overlaps a corresponding fold of the other valve, with some 

 matrix intervening. Where broken, this arrangement has the appearance of a 

 gutter filled with dry mud. It is not subcyliudrical as in the analogous structure 

 in L. senigmatica (Fig. 12, page 199), but flattened. As a junction of the two 

 valves, it is not compatible with a free motion of one or the other; but rather 

 indicates a nearly flat and shield-like condition of the carapace. The upper 

 part of this flat gutter-like hinge-structure may possibly be homologous, in some 

 degree, with the middle piece in the Bhinocaris and Mesothyra of North America. 



On the surface of the valve four or five oblique folds of limited extent mark 

 the anterior moiety; and the remainder seems to be smooth, except for some very 

 faint striae, which are far better pronounced in Fig. 15. There is a definite 

 posterior elongation of the dorsal border, as a stout process, not unlike, but more 

 slender than, that shown in Fig. 12 a. It has been almost lost in Fig. 15. 



2. The other counterpart (Fig. 15) is more imperfect at the ends than Fig. 14, 

 and measures 55 mm. by 15 mm. It agrees with Fig. 11 in general shape, and in 

 showing a straight and peculiarly folded dorsal margin. The short oblique 

 crumpling, on the front part of the valve, and the little rough ridge (impression) 

 near the ventral margin, and which may represent the mesolateral in Dithyrocaris, 

 are characteristic. The surface also exhibits numerous delicate, curved, parallel 

 striae, starting as it were in the antero-ventral region, at first crowded, and nearly 

 parallel with the ventral edge, but turning upwards and backwards, and feathering 

 off, with widening interspaces, towards the dorsal border. This delicate sculp- 

 turing must have been nearly lost on the other counterpart (Fig. 14) by the 

 removal of an outer film of the shell. 



1 A specimen consisting of two counterparts, and in so far analogous to Figs. 14 and 15, was 

 figured in PL XXI, figs. 7 a, 7 b, and described at p. 158 as casts of the left-hand moiety of a cara- 

 pace of probably Dithyrocaris Scouleri. 



2 Somewhat like that of Rhinocaris bipennis, J. M. Clarke, ' Geol. Survey State of Xew York,' 

 1896, p. 09. 



