So6 



STICTODISCUS. 



GENUS 170. 



b 



STICTODISCUS GREV., 1861. 



Valve disciform or angular, 

 with median portion inflated, 

 inflation unequal in the two 

 valves ; centre more or less 

 hyaline ; the remainder of the 

 valve more or less strongly 

 punctate, puncta arranged in 

 radiant rows, separated by 

 plicae. 



Fig. 254. Stictodiscus. 



a. S. Kittoniatius f girdle face J. 



/'. 5. Johnsonianus (valve). 



This beautiful genus includes about 50 species, the greater number of 

 which are fossil. In the text will be found, after Greville, the valve of S. 

 Johnsonianus Gr., and the girdle face of S. Kittonianus Gr. These two species 

 are fossil, the first is found in the Naparima deposit (Trinity Island), the second 

 in the deposits of South America, specially Nottingham, Richmond, &c. 



GENUS 171. ARACHNOIDISCUS EHR, 1849. 



Fig. 255. Arachnoidiscus ornatus. 



