426 



PYRGODISCUS. 



Fig. 143. Pyrgodiscus armatus. 



GENUS 92. PYRGODISCUS KITTON, 1885. 



Valves orbicular, fur- 

 nished with punctate lines, 

 regular, radiant ; showing 

 a high central elevation, 

 usually with eight angles, 

 terminated by the same 

 number of very robust, 

 erect spines ; with margins 

 furnished with eight eleva- 

 tions, each crowned with a short robust awn, alternating with the 

 spines of the central elevation, and connected with it by a ridge, or 

 smooth, elevated line. 



This genus was created for the fossil form P. armatus Kill., represented 

 in the figure in the margin (fig. 143), which is found in the marl (Tegel) from 

 Briinn, in Moravia, and which is characterised by its size, which attains to 8 

 to 10 c.d.m. in diameter, while the P. simplex, afterwards created by Dr. O. 

 Witt, is much more delicate, and hardly reaches in diameter the moiety of the 

 preceding. It is found in Simbirsk. 



Dicladia Ehr., 

 1844. Frustule com- 

 pressed, with sutural por- 

 tion narrow, furnished 

 with horns, more or less 

 elongated, often ramous 

 or furcate. Valves 

 sometimes short and 

 obtuse, at other times 

 furnished with short, 

 _ _. . ,. _ . , . scattered spines. 



Fig, 144. Dicladia Caprcolus Ehr. * 



Dicladia Caprcolus (fig. 144 in margin), is the best known species of this 

 genus. It is frequently met with in the living state (amongst others by Mr. 

 Norman, in Ascidinus, off Hull), and in guanos and fossil deposits (Peters- 

 burgh, Naparima, Richmond, etc.). According to the observations of Count 



