234 EEV. J. F. BLAKE ON THE 



champs, from the Kimmeridge Clay ; but the spines on the more 

 convex valve are far less numerous, and they are not produced into 

 tubes. It differs from P. virgulina, Et., in its shape and the length 

 of the spines. Plicatulw all look so much alike that few venture to 

 name them ; there can be little doubt, however, that this is dis- 

 tinct. 



It is rather common in the lower beds of the Portland Stone, as 

 in the creamy limestone of Quainton. 



Lima bifurcata, spec. nov. 



I have not sufficiently good materials to illustrate this species ; 

 but it seems to me a distinct one. The two valves have very little 

 convexity ; and the general shape is like that of Lima rudis, but 

 more quadrate. It has, in the cast, great rounded ribs, which to- 

 wards the end bifurcate into two smaller ones, and this is its dis- 

 tinguishing feature. 



It is not uncommon in the rubbly limestones of Coney Hill and 

 Aylesbury. 



Pecten Moeini, De Loriol. PI. X. fig. 3. 



This characteristic Portland-sand fossil is distinguished by its 

 bifurcating punctated striae, which are very close-set. 



Ehtn-chonella poetlandica, spec. nov. PI. X. fig. 8-8d. 



Shell longer than wide, outline irregular, beak prominent ; fora- 

 men of moderate size, its lower half bounded on each side by the 

 deltidium. Imperforate valve very convex at first, short, sloping 

 down in two long tongues and having three nearly obsolete ribs 

 on each side, in addition to the median elevation. Perforate 

 valve convex in the middle line at first, but soon bending round 

 at right angles into a long tongue, so as to be concave from 

 side to side ; this tongue is generally simple, as in B. acuta, but 

 appears to be variable, some having it bifid, or even trifid, but differing 

 in no other respect from the type. There are ribs on each side of 

 this valve corresponding to those on the other. There are no longi- 

 tudinal riblets on this species, though the lines of growth are clearly 

 seen. One can scarcely feel quite certain whether this is a distinct 

 species from E. suhvariahilis. That species comes from the Kim- 

 meridge Clay of Pottern, "Wilts, which is the equivalent of the 

 Swindon and Hartwell clays, and therefore very little removed in 

 time, if at all, from the deposits whence these are derived. These, 

 too, have a singular resemblance to JR. variabilis of the lias. The 

 distinguishing features, as compared with the Kimmeridgian form, are 

 (1) the greater inflation of the shell, so that a side view shows a 

 triangle whose base is as great as its altitude ; (2) the prevalence of 

 one central fold only ; (3) the smoothness of the surface ; (4) the 

 larger foramen. It is also very near to B. HoJieneggeri, Suess, but 

 is more quadrate ; and the latter, though common, is not found with 

 a single fold. 



Common in the lower part of the Portland Sand at Black Yen, 



