162 JURASSIC BIVALVIA AND GASTROPODA 



stronger and more numerous. In all four specimens crushing has increased the 

 apparent angle of the spire when one of the flattened sides of the shell is viewed, but 

 deformation of this nature does not seem to be entirely responsible for the consider- 

 able difference in the height of the whorls. 



Pietteia dusseensis sp. nov. 

 PI. 27, figs. 16a, b, c 



Diagnosis. Shell rather small (height of holotype c. 13 mm.), spire moderately 

 broad, its angle about 25 °. Protoconch unknown. Preserved whorls with a 

 flattened, vertical outer face separated by a rounded-off angulation from a broad 

 sutural ramp which forms an angle of about 45 ° with the axis of the shell. Orna- 

 ment, except on later part of last whorl, consisting of rounded collabral ribs and of 

 fine spiral threads overriding them ; the ribs, which are most prominent at the ramp 

 angle, where some swell out to form tubercles, are separated by intervals about three 

 times as wide ; the number on the penultimate whorl is about 12. The terminal 

 rib is particularly prominent, constituting a varix. Later formed part of last whorl 

 without ribs, but with a single prominent tuberculate carina at the ramp angle, 

 which forms the periphery ; base convex just below periphery, but well excavated 

 at the beginning of the neck of the shell ; spiral threads, separated by broader 

 intervals, are present on the ramp of the last whorl and on the base. Aperture 

 and rostrum not preserved ; the cross-section of the proximal part of a single 

 broken-off labral digitation is seen in the holotype. 



Holotype. No. G. 76405. The only specimen. 



Locality and horizon. Dusse, i\ miles S.E. of Rahmu, N.E. Kenya ; Upper 

 Oxfordian, Seir Limestones. 



Remarks. This species is referred to Pietteia on account of the nature of its 

 ornament and of the evidence that a single stout labral digitation was present. No 

 closely comparable Upper Jurassic species can be cited. The French Bajocian 

 species Pietteia rarispina (Schlumberger) (Piette 1867 : 100, pi. 20, figs. 1-3) is more 

 slender and lacks tubercles on the peripheral carina of its last whorl. Such tubercles 

 are found on its contemporary species P. lotharingica (Schlumberger) (Piette 1867 : 

 105, pi. 21, figs. 1-11), which, however, is a much more slender shell. 



Genus HARPAGODES Gill 1869 



Harpagodes aff. oceani (Brongniart) 

 PI. 28, fig. 3 



1821. Aff. Strombus Oceani Brongniart : 554, 570, pi. 7, fig. 2. 



18676. Aff. Pterocera Oceani (Brongniart) ; de Loriol : 40, pi. 4, figs. 4, 5. 



1 891. Aff. Harpagodes Oceani (Brongniart) ; Piette : 456, pi. 45, figs. 1, 2 ; pi. 48, fig. 1 ; 



pi. 65, figs. 5—7 ; pi. 80, fig. 1 ; pi. 8i, figs. 1-3. 

 1910. Aff. Strombus Oceani Brongniart ; Lemoine, pi. 176. 



Material. Four specimens (nos. GG. 10319-22). 



