Prof. T. R. Jones 8^ H. Woodward — Falceozoic Fhylhpoda. 543 



triangular ridge between two furrows ; or as two small ridges 

 bounding a triangular pit; or otherwise modiBed. 



The straight edge of the long (posterior) portion of the valve has 

 a corded appearance, from a little below the umbo to the extremity. 

 This special margin begins very thin, and widens downwards, the 

 little cross-strise or wrinkles becoming stronger as it widens ; the 

 last eight or ten are much larger and thicker. In some cases (as in 

 Fig. 9, more especially) it is double. Possibly this corded margin 

 has reference to a peculiar dorsal longitudinal plate intermediate to 

 the two valves. This may have been susceptible of being bent 

 when the valves closed ; or it may have split along its length. 

 Such an intermediate dorsal plate is regarded by Hall and Clarke as 

 having existed in Mesothjra (" Palseont. New York," vol. vii, 1888, 

 p. 187, pi. xxxii, fig. 1) ; but we do not find it in the allied Bithyro- 

 caris. The corded margin has a distant analogy to a lateral moiety 

 of the intermediate and striated plate in Fholadocaris, H. Woodward 

 (Geol. M^g., Dec. II, Voh IX, 1882, p. 388, PI. IX, Fig. 16). It 

 more closely resembles the much stronger, corded, dorsal edges in 

 Dithyrocaris tricornis, H. W. and E. Eth. (Geol. Mag., Vol. X, 1873, 

 pp. 483-6, PL XVI, Fig. 3), which does not seem to possess an 

 intermediate dorsal plate. Fholadocaris has been met with only in 

 its expanded form; but Dithyrocaris has been found both in the 

 expanded and closed state. 



The two valves of Finnocaris, if placed side by side, with the 

 straight edge of one in contact with that of the other, vs^ould present 

 an analogy to some of the flat open carapaces of Fholadocaris and 

 Aptychopsis, with the difference that there would be little or no 

 nuchal notch with the two valves of Finnocaris thus arranged, and 

 a very narrow open space below the umbo, not gaping at the end. 



Judging from the two outlines of the counterparts of the closed 

 carapace (PI. XV, Figs. 8 and 9), we may say that when the valves 

 were closed the dorsal edges would lie against each other (with or 

 without a very narrow flanging ligament), whether they formed 

 a straight or a slightly flexuous line, with or without a protruding 

 umbo. Even anteriorly the edges would meet (with a slope), and 

 would not necessarily require an intermediate plate. So a bivalve 

 Mollusc, if laid open, would have angular notches fore and aft, but 

 no intermediate plates. 



As far as mere outline is concerned, Finnocaris has a distant re- 

 semblance to a figure of Beecherella suhtumida in E. 0. Ulrich's 

 memoir on that genus, "American Geologist," vol. viii, 1890, p. 

 200, pi. ii, fig. 6 ; but it is very distinct in other respects. Tlie 

 ■ outline may be said to have a still more remote likeness to Fro- 

 tozoea Hifgendorfi, Dames, " Zeitsch. d. Geol. Ges.," vol. xxxviii, 

 1886, p. 577, pi. XV, figs. 5-7. 



Except one example from the Upper Silurian of Kendal, West- 

 moreland, all the specimens we have seen are from the Lower 

 Silurian of Girvan, Ayrshire, from which locality Mrs. Gray, of 

 Edinburgh, has made a large collection. 



