292 DESCBIPTION OF {Polygastrica. 



a specimen of Anuraa, wliicli, together with yellow i)hopphore8cent 

 species of Peridinea, were li\'ing in the same water ; but no direct 

 evolution of light was observed from M. octoccros." Size l-280tLi 

 without the spines ; with the spines 1-2 10th. 



Genus LiTHODESMruM. — Lorica simple, univalved, siliceous, and 

 triangular in shape. Self-division imperfect, the creatures being 

 clustered in the form of straight and rigid triangular-shaped wands ; 

 cluster unattached. 



This genus was named and described by Elirenberg, in 1840, as 

 belonging to the family Besmidiece ; however, this alliance would, 

 from the illustration given, appear very doubtful. 



L. undulatiim. — Coi-puscles large, smooth, and pellucid; the angles 

 obtuse. Two of the sides are undulated, the others doubly excised; 

 openings and motion are not perceptible. The corpuscles are some- 

 what longer than they are broad. Found alive, in sea- water, at 

 Cuxhaven. Greatest length of corpuscle, l-480th. (P, 13. f. 

 41, 42.) 



Genus Exjcampia. — Lorica univalved, wedge-shaped, and flat, 

 excised in the middle of its lateral surfaces. Self-division being 

 imperfect, the creatures are clustered in the form of flat articulated 

 chains, having roimdish holes between adjoining segments, the 

 cui'ved chains gradually becoming circvQar ; cluster unattached. This 

 is another questionable genus of Desmtdiacea, described by Ehrenberg 

 in 1840. 



E. zodiaca. — Lorica ciystalline, smooth, a little longer than it is 

 broad ; ova of a light yellow colour. Locomotion not perceptible. 

 Found alive in sea water, at Cuxhaven. Diameter 1-1 150th. 

 (P. 13. f. 43.) 



Genus Odontella (Ehr.) — The tooth-cliainedAnitnalcuhs comprised 

 in this small genus are unattached and free, having a simple uni- 

 valved compressed lorica, and multiply by an incomplete spontaneous 

 self-division, in the form of flat articulated ribbons or chains ; each 

 link of such chain-like bodies is composed of a single pair united, 

 which are connected with the next pair by two processes, a small 

 space being left between them (see f. 108), and hence they difier 

 from the genus Desmidium. The internal coloui'ed gi-anular matter is 



