XANTHIDITJM. 93 



X. i;i-i:\ai:hm, Ehrb. Plate XXIII, figs. 7. 8, 0. 



Cells in front view broader than Long; constriction deep, 

 sinus acute angled; spinous; spines subulate, marginal, gem- 

 inate; central projection somewhal truncate and margined 

 with pearly granules. 

 1 tiameter 65-73 //. 



West Point, N. Y. (Bailey. . 



Halt'- suL r irt-ts that this is the -ami' as his .V. Brebissonii. 



The Dumber of spines appears t>> he variable. Bailey and 



Ehrenberg'a figures have -i\ pair- of -|>iin->. Brebis-on's. 



Jit : whilst some British specimens bave ten t<> each semicell. 



K. cbistatum, (Breb.) Ralfs Plate XXI, figs. 6 B 



Semicells with a solitary spine on each side at the base, the 

 other spines geminate, in four pair-. Central protuberance, 

 -hurt conical. 



1 >i;i 1 1 1. t < i h i ">.") n. 



Pennsylvania, New Jersey, South Carolina, Georgia, etc. 



X. asteptum, Nord. Plate 21, figs. '.. 10, 11. 



A 1 . h 1 1 one-fourth longer than wide; semicells octangular- 

 oval, or truncate-triangular with two diverging, somewhal 

 curved, subulate spines on each side, and two geminate -pines 

 at each of the two superior angles. Cytioderra smooth or 

 punctate. 



Diameter K) 48 y. without the spin 



Rather rare; quiet waters, Pennsylvania and New Jersey. 



X. fasciculatum, (Ehrb.) Ralfs. Plate XXII, figs. 4, 5. 



Semicells with four, rarely six pair- of long, subulate, 

 marginal, spreading -pines; central projection, minute conical, 



not headed. 



Diameter 55-65 (i. without the -pin.-. 



Yar. BEXAGONUM, Wolle. Plate XXIII. fig. 5. 



Large angular, with tour pair of short subulate spines. 



Yar. minor. Wolle. Smaller in -ize, and -pines short. 



Plate XXII, figs. <i, 7, front and lateral view of a semicell 

 which appears to develop a sporangium without copulation. 

 1 found but one specimen of the kind, and record it as a pecu- 

 liar abnormal act. 



