350 PROF. T. R. JO^TES ON THE OSTEA.CODA 



high on the back at the anterior third, where the front hinge 

 somewhat projects. Edge-^iew blunt, compressed oval. Surface 

 coarsely pitted with a rough reticulation. Ventral edge much 

 incurved. 



Eound at Swindon (specimen no. 364), in Purbeck beds, by the 

 Rev. Prof. J. P. Blake, P.G.S., after whom it was at first named 

 (when this paper was read) ; but another Cythere had already been 

 assigned to him. C. traiwiens occurs also in a soft, white Portland 

 stone from Brill. 



14. Cytheee eetzrtj&ata, sp. nov. (PI. IX . figs. 17-24, including 

 var. rugidata, figs. 17-20 ; and var. textilis, fig. 24.) 



Length usually | mm., fig, 19, J mm. 



Suboblong, with oblique ends, sloping from the front and hinder 

 ends of the hinge-line, which is straight, and oblique to the long 

 axis of the valve. Ventral border slightly sinuous, and much 

 incurved at its edge. Edge-view oval, slightly acute. Surface pitted 

 over two thirds of its area, and wrinkled or finely costulate along 

 the ventral region ; the pits in fig. 17 (var. rugidata) are wide apart 

 and roundish ; in other specimens (fig. 21) they take a rough 

 reticulate pattern (retirugata) ; and in others (fig. 24) the reticulation 

 is delicate (var. tecctilis), the meshes are open, with thin walls, and 

 become regular and rectangular on the ventral region, where the 

 longitudinal mesh- walls represent the riblets of other specimens. 



At first I was inclined to separate figs. 17-20 off from the others 

 as a distinct form (C. rugidata) ; but the gradation to fig. 21 is 

 evident, and Dr. Gr. S. Brady has suggested that it may be the male 

 form : nevertheless it will be convenient to keep rugulata as a 

 varietal name. The pattern of fig. 24 is the same as that of the 

 foregoing, although in detail the reticulation is more like lace-work, 

 the meshes being much finer, and the costulation far more delicate. 

 The last deserves a varietal name, textilis. 



In figs. 17-20 each pit seems to open inwards in a little tube ; 

 and each mesh in figs. 21-23 has two or more of such little 

 perforations. 



C. retirugata (type) was found in specimen no. 253 (figs. 21-23), 

 from HartweU ; and no. 364 from Swindon (Prof. Blake). 



G. rugulata in four specimens, nos. 256 (figs. 17, 18), 258 (fig. 20), 

 269 (fig. 19), and 357, all from HartweU. 



C. textilis, also from HartweU (Barnard's pit), specimen no. 166 

 (fig. 24), and from BriU. 



