492 



PERITHYRA. 



GENUS 155. PERITHYRA EHR, 1854. 



Valves circular, with fine puncta arranged 

 in radiating rows, and with coarse marginal 

 tubercles. 



This genus, which appears rather doubtful, 

 includes, according to Ehrenberg, two forms, P. 

 denaria Ehr. (fig. 230) and P. quarternaria Ehr., 

 which only differs in having four tubercles. These 

 torms are found in the Ganges. For anything I 



Fig. 230. 

 Perithyra denaria, 



know, they have never been seen by anyone but Ehrenberg 



GENUS 156. MICROPODISCUS, GRUN., 1883. 



Fig 231. 



Micropodiscus 

 Weissflogii. 



Valve with margin furnished with a circlet of 

 dots (or small awl-shaped spines) and of a small 

 elongated process. Puncta very fine, indistinctly 

 radiant ; a circle of coarser dots near the central 

 portion. 



A single species. 



M. Weissflogii Grun. ! (in H.V.H.'s Types, Nos. 11 and 416), 

 fig. 231 in the text. 



Characteristics of the genus ; the awl-shaped spines of the circlet 10 to 

 13 in 1 c.d.m. Diameter, "5 to 1*5 c.d.m. 



Brackish w<~ter Blankenbei-CThe. 



