194 bulletin: museum of comparative zoology. 



Possibly an older form of A. spinosum. Intermediate stages not, however, 

 observed. Transdiameter of midbody, 40 p ; length of spines, 35 /i. 

 Station, 4722. 



Acanthodinium spinosum, sp. nov. 



Plate 11, Fig. 66. 



Axial length of body (without spines) 1.1-1.2 transdiameters of girdle. 

 Dorso-ventral and transverse diameters equal. Epitheca less than hypotheca. 

 Altitude of epitheca 0.3-0.4 of the axial length from the apex. Transverse 

 furrow very lightly indented, its proximal and distal ends not displaced. 

 Longitudinal furrow short with low lists. Epitheca with small circular area 

 about apical pore. Apical plates without spines. Dorsal and ventral apicals 

 narrow, laterals very wide. Of the eight precingular plates the two midven- 

 trals are small, and the remaining six are large, subequal, and bear centrally 

 located spines. The two laterals are often without spines. 



In the hypotheca the plates are less regular. The two antapicals are un- 

 equal in size and may bear spines. The six postcingulars are also unequal, the 

 left midventral being smaller and the others increasing in size to the right. 

 The longitudinal furrow plate consists of a larger posterior and smaller an- 

 terior moiety. Spines have been found on all plates of the hypotheca excepting 

 only the furrow plates and the left midventral postcingular. Spines 0.4-0.6 

 transdiameters at girdle in length, slightly curved conical, tapering evenly, to 

 a sharp point, with one central pore canal. Suture lines marked by single, 

 rarely doubled, ridges. Thecal wall porulate. Plates usually bordered by a 

 peripheral pore-free band. 



Length, 45 /i; diameter at girdle, 40 /x; length of spines 16-25 /u. 



Stations, 4707, 4722. 



This is the type of Acanthodinium. 



Phalacroma lenticula, sp. nov. 



Plate 12, Fig. 69. 



A medium-sized species with lenticular body, very high epitheca, and finely 

 reticulate wall. 



Body lens-shaped, much compressed laterally, its transdiameter less than 

 0.25 of the dorso-ventral, nearly circular in lateral view, the dorso-ventral 

 width of the body exclusive of the fin, 1.06 times the length, the longest antero- 

 posterior axis being slightly oblique (10° antero-dorsally) to the girdle. The 

 epitheca is unusually high, nearly equalling the hypotheca in length. The 

 girdle is narrow, furrow not impressed, with low fins. Left ventral fin with 

 two ribs, the right low, reticulate at the base. 



Thecal wall finely reticulate, about 16 mesh on the radius at the girdle, 

 minutely porulate. 



Length, 81 /x ; dorso-ventral diameter, 86 p. 



Station, 4749. 



