84 JURASSIC BIVALVIA AND GASTROPODA 



Remarks. The hinge-teeth are not seen in any of the specimens but there is 

 little doubt that the species is an Astarte. It is more quadrate in outline and less 

 strongly inequilateral than A. lurida, recorded above. A. camertonensis Moore 

 (1867 : 213, pi. 7, fig. 21), from the Pliensbachian of England, is more elongate. 



Astarte didimtuensis sp. nov. 

 PL 12, figs. 10a, b, c, 11a, b, c 



Diagnosis. Small (length of largest specimen c. 12-5 mm.), ovate, inequilateral ; 

 height three-quarters to four-fifths of length, beaks from anterior fifth to quarter of 

 length ; inflation moderate. Umbones subangular, not incurved, prosogyrous ; 

 postero-dorsal outline straight, subhorizontal, meeting the strongly convex posterior 

 margin in an even curve which is continued by the strongly convex ventral and 

 anterior margins ; antero-dorsal outline strongly concave. Lunule moderately 

 impressed ; escutcheon narrow and shallow. Ornament consisting of fine, equal 

 concentric riblets which may show slight irregular undulations on posterior part of 

 surface. 



Holotype and paratypes. Holotype, no. LL.35032 ; 9 paratypes. 



Locality and horizon. Didimtu hill, 2 miles S. of Bur Mayo, N.E. Kenya ; 

 Upper Lias, Toarcian, Didimtu Beds. 



Remarks. Astarte didimtuensis is more elongate and has finer concentric orna- 

 ment than its associated species A . subminima, described below. It is quite unlike 

 A. voltzii Roemer (1836 : 112, pi. 7, fig. 17), the common small astartid of the 

 European Upper Lias, differing in its more elongate and much more compressed 

 form and in the even distribution and fineness of its concentric threads. 



Astarte subminima sp. nov. 

 PL 12, figs. 14a, b 



Diagnosis. Small (length c. 6 mm.), subtrigonal with an orbicular tendency, 

 inequilateral ; height and length almost equal ; beak at about anterior quarter of 

 length ; inflation weak. Umbo sharply rounded in outline, not incurved, slightly 

 prosogyrous ; postero-dorsal outline slightly convex, gently sloping, forming a well- 

 marked, obtuse angle with the rather low, straight, subvertical posterior margin ; 

 ventral margin strongly convex, meeting posterior margin in an ill-defined, obtuse 

 angle ; anterior margin low ; antero-dorsal outline concave, steep. Lunule 

 moderately impressed, no escutcheon. Ornament consisting of fine, equal con- 

 centric ribs. Ventral margin denticulate internally. 



Holotype. No. LL. 35042. The only specimen. 



Locality and horizon. Didimtu hill, 2 miles S. of Bur Mayo, N.E. Kenya ; 

 Upper Lias, Toarcian, Didimtu Beds. 



Remarks. This species is rather similar to Astarte minima Phillips, from the 



