508 DE8CEIPTI0N OP {Polygasirircc 



Bistiug of nine cells, of which four are exterior (marginal), and 

 surrounding other four, having the remaining one in the centre. 

 Diameter 1 -600th. Caltanisetta. Fossil. 



DiCTYOCHA triacantha. — Regularly triangular, with spinous angles ; 

 marginal cells three, unarmed on their inner border. Diameter 

 1- 864th. Maryland. 



D. tripyla. — Unequal, with three unarmed cells prolonged as rays 

 to the middle; four irregular marginal, cells with spines. Diameter 

 1 -492nd. Oran. 



D. uhera. — Hexangular ; seven marginal cells, and six spines ; the 

 two central cells unarmed. Diameter 1 -600th. Maryland. 



Ehrenberg appends the following remark to the description of the 

 sixteen immediately preceding species, "I have studied to dis- 

 tinguish the forms of this genus, but have not yet been able to 

 determine species and varieties." 



D. hemispherica. — Hemispherical but hexagonal in outline, with 

 six lateral spines ; six opposite marginal cells with spines, and six 

 internal cells surrounding a central one; the lower aperture half 

 closed by six marginal teeth. Diameter l-744th. Bermuda. 



D. Ponticulus. — Lanceolate-oblong, divided by a simple transverse 

 median arch into two cells ; margin unarmed. Diameter l-432nd. 

 Bermuda. 



D. Quadratum. — Quadrate or subquadrate, oblong; divided into 

 two cells by a simple median arch ; a single spine on each side. 

 Diameter 1 -480th. Bermuda. The two preceding forms were first 

 observed and figm-cd by Dr. Bailey of New York. 



D. hiternaria. — Habit of D. aculeata, with short spines and six 

 marginal cells, of which three are larger and adjoin the three others; 

 consequently, not alternating ; no median cell. Diameter, without 

 spines, 1 -432nd- Antarctic Ocean. 



D. octonm'ia. — Habit of D. ornamentum of Sicily, with eight 

 spines, one larger than the rest ; marginal cells irregular, fewer in 

 number at that part where the spines are increased, and with a very 

 large central cell. Diameter, exclusive of spines, 1-1 152nd. If a 

 monstrous variety of D. ornamentum ? 



D- ahnormis. — Quadrangular, with spinous angles ; five internal, 



