FOSSILS. 609 



transverse to the dorsal margin and a little nearer the anterior side. 

 The anterior ridge consists of a single highly elevated, rounded or 

 papillose tubercle near the dorsal margin, and an elongated elliptical 

 tubercle placed obliquely near the antero-ventral margin, and in older 

 specimens sometimes swelling and spreading over the margin. The 

 posterior ridge rises near the dorsal margin, and making a slightly 

 broader curve than the posterior end of the valve approaches the 

 ventral margin at the centre : the ridge is high and angular with a 

 small prominent tubercle at the dorsal extremity, and from four to six 

 smaller spine-like tubercles along its curve. The central ridge or tuber- 

 cle is separated from the lateral ridge by a distinct furrow, and its con- 

 tinuation from the base of the tubercle passes between the lower ends 

 of the two lateral ridges. Ventral and lateral margins with a narrow 

 thickened rim. 



This species resembles very nearly the B. tuberculata of Kloden, as 

 described and figured by Mr T. Rupert Jones. In our specimens the 

 dorsal angles are more rounded ; the posterior ridge at its base is 

 never extended beyond the middle of the valve, and is marked on its 

 crest by several small spine-like tubercles. The anterior ridge is 

 usually more extended along the ventral margin in our specimens, 

 and the furrow is better defined, while the tubercles are never flattened 

 above or overhanging the base as shown in the European specimens. 

 Smaller specimens, which appear to be the young of this species, pre- 

 sent some slight variations of surface markings, but show less difference 

 than the young of B. tuberculata. Arisaig, coll. J. W. D. 



Fig. 216. — Beyrichia pustuloses Fig. 217. — B. equilatera. 



e- 



§ 



Beyrichia equilatera, Hall (Fig. 217). Nearly equilateral, very 

 convex, marked by three smooth or nearly smooth ridges. The 

 central ridge is an oblong tubercle reaching from near the dorsal 

 margin a little more than half way to the ventral margin. The pos- 

 terior ridge is a little larger, but scarcely differing in form from the 

 anterior one, its ventral extremity terminating beneath or a little in 

 advance of the middle of the central tubercle. The furrow is narrow, 

 but well defined on the two sides of the central tubercle, and becoming 

 shallow in its passage to the marginal furrow ; ventral and lateral 

 margins thickened. Arisaig, coll. J. W. D. 



Leperditia sinuata, Hall. Minute, sub-ovate, anterior end narrow, 

 dorsal line one-third shorter than the length of the valve ; an extremely 

 minute tubercle near the anterior end. Centre extremely convex or 



2 B 



