60 JURASSIC BIVALVIA AND GASTROPODA 



from the Bathonian, but not one where the recorded specimens are illustrated can be 

 accepted. The specimen figured under this name by Morris & Lycett (1853, pi. 3, 

 fig. 3) has been made the type of a new species L. bynei by Cox & Arkell (1948 : 17) 

 and has fewer ribs than the form now described. Weir (1938, pi. 4, fig. 16) has 

 figured a specimen from the Kambe Limestone (Upper Bajocian or Bathonian) of 

 Kenya as L. cf. semicircularis. Its ribbing has been largely removed by erosion, but 

 its outline resembles that of the species now described. 



Lima {Plagiostoma) cf. schardti de Loriol 



1883. Cf. Lima schardti de Loriol : 71, pi. 10, figs. 5— 11. 



i960. Lima (Plagiostoma) cf. schardti de Loriol ; Joubert, pi. 8, fig. 3. 



Material. Several imperfect specimens. 



Localities and horizons. Hills S. of Melka Murri-Rahmu road, 13 miles W. of 

 Rahmu, N.E. Kenya ; Callovian, Rukesa Shales. Kulong, 2 miles S.W. of Muddo 

 Erri, N.E. Kenya ; Callovian [?-Lower Oxfordian], Muddo Erri Limestones. 



Remarks. In this species, originally described from the Mytilus Beds (Bathonian- 

 Callovian) of Switzerland, the valves bear about 26 scaly ribs separated by intervals 

 which are of the same width as the ribs over the greater part of the surface but become 

 wider than them near the ventral margin. The ribs cannot be counted exactly in the 

 specimens now recorded but their spacing is exactly as indicated in de Loriol's figures 

 and their scaly character can be seen in places. The general outline of the shell is 

 also as indicated by de Loriol. 



Lima {Plagiostoma) muddoensis sp. nov. 

 PI. 8, fig. 2 

 i960. Lima (Plagiostoma) cf. complanata Laube ; Joubert, pi. 8, fig. 5. 



Diagnosis. Of small-medium size (height of holotype c. 35 mm.), trapezoidal, 

 length and height almost equal ; inflation rather weak in holotype, but this is 

 probably partly due to compression in fossilization. Ventral margin moderately 

 asymmetrical ; umbonal region not protruding, very slightly obtuse in outline, its 

 angle about 100 ° ; anterior umbonal ridge rounded off, straight, forming an angle 

 with the hinge-line which slightly exceeds 45 °. Lunule scarcely excavated. Poste- 

 rior auricle relatively large, its outer angle only slightly obtuse ; anterior auricle not 

 seen. Main surface bearing about 30 prominent, rounded ribs which are equal in 

 strength and appear smooth except in late stages of growth, when they bear trans- 

 verse imbrications. Intervals about same width as ribs and apparently without 

 punctations. Posterior auricle with about 6 nodose radial ribs. 



Holotype. No. L. 92065 ; the material examined includes about two other 

 specimens which probably belong to the same species but are too imperfect to rank 

 as paratypes. 



