MM. Jones and Kirkby — Carboniferous Ostracoda. 437 



5. Beyrichiopsis subdentata, sp. nov. PI. XL Figs. 1, 2. 



Along with B. fimbriata in the Plashetts shale are numerous 

 examples of another form, having longitudinal ribs, a reticulo- 

 punctate surface, and occasional traces of denticles on the ventral 

 and posterior borders. 



It is smaller than B. fortis, but of similar outline, and with the 

 valves lobed much in the same manner. A sinuous rib passes 

 across the lower half of the valve concentric with the ventral and 

 extreme borders ; and a short dorsal rib is sometimes present on the 

 posterior half. The surface is regularly, and somewhat coarsely, 

 punctate, rather than reticulate. The posterior half of the free 

 margin of some specimens is denticulated, but there are no traces of 

 a fully-developed fringe. Length, ^V inch. 



We have examined many valves of this species, but can find 

 nothing to show that it ever possessed a perfect fringe. The valves 

 we meet with of fimbriata and fortis very often are without this 

 appendage; but this is accidental, for close examination invariably 

 shows where it has been broken off, by removal from the matrix or 

 otherwise. In subdentata, however, the margins show no indication 

 of fracture, and they are evidently found as they were originally. 



Locality. — Calciferous-Sandstone series. Plashetts, Northumberld. 



Neither of the last two species exactly agree with our definition 

 of the genus : B. cornuta having the marginal fringe, but not the 

 longitudinal ribs ; B. subdentata possessing the latter character, but 

 the fringe only in a very incipient state. Still we are inclined to 

 look upon them as belonging to the same natural group as the others, 

 though less advanced perhaps in the process of differentiation from 

 Beyrichia. In fact, by taking another and less elastic view of the 

 subject, it would be easy to look upon all the forms as but the varietal 

 or individual differences of one species ; for they certainly run very 

 near to each other. This, however, would scarcely be in accordance 

 with modern biological ideas ; nor could we ignore the probability 

 of the soft parts of the various forms having differed materially one 

 from the other. 



6. Beyrichiopsis simplex, sp. nov. PI. XII. Fig. 4. 



A very short time ago, Mr. Hugh Miller, of the Geological Survey, 

 sent us a series of Ostracodous specimens from the Carboniferous 

 rocks of Northumberland. Among them is a fringed form from the 

 Lower Carboniferous of Warksburn, North Tynedale, that appears 

 to be different from those already described. It occurs in single 

 valves, imbedded in a matrix of dark grey shale, along with species 

 Kirkbya, CythereUa, and other marine fossils. 



It has a neat Beyrichian outline, with rounded extremities and a 

 convex ventral margin. The anterior portion of the valve is much 

 higher than the posterior. There is a well-marked subcentral sulcus, 

 with a round, but rather faint boss in front. The surface has no ribs ; 

 but is sparsely and finely granulated. A narrow fringe bounds the 

 free margin, and breaks up into spines posteriorly, as in other species ; 

 and at the base of the fringe runs a beaded line. Length, -^ inch. 



