404 



BULLETIN 100, UNITED STATES NATIONAL MUSEUM 



tremocyst, bordered by a line of small, spaced pores, ending distally 

 in a peristomie more or less developed. The apertura is semielliptical, 

 transverse; the peristome is thin and garnished by four distal spines. 

 The ovicell is globular, of the same structure as the frontal and 

 opens above the operculum; the aperture of the ovicelled zooecia is 

 larger than the others (0.10 by 0.15 mm.). The ancestrula is mem- 

 braniporoid and surrounded by 10 spines. 

 Measurements. — 



=0.09 mm. . J Lz -0.60-0.75 mm. 



:0.12 mm. zooecia Zg _ 0>40 _ 0-50 mm< 



Apertura , 



T K 



Fig. 156. — Genus Perigastrella Canu and Bassler, 1917 

 A-E. Perigastrella conlracta Waters, 1899. A. Zooecia, X25. B, C. Opercu- 

 lum and apertura, X85. (A-C after Waters, 1899.) D, E. Zooecia and aper- 

 tura. (After Norman, 1909.) 



F-L. Perigastrella labiata Boeck, 1861. F. Zooecia showing the marginal pore 

 and the spout-shaped projection towards the aperture. G. Basal view of the 

 zooecia showing the arrangement of the dietellae. H. Upper part of a zooecium 

 in basal view. I. Lateral view of a zooecium. J. Lateral view of an ovicell 

 and the upper part of a zooecium. K. Aperture with oral spines. L. Base of 

 an ovicell. (F-L. After Levinsen, 1916.) 



Affinities. — The measurements are quite variable and the marginal 

 cells are very large. The ancestrula is variable; when it is small it 

 presents only an orifice surrounded by spines; if it is larger it has a 

 real orifice and a membranous frontal. 



This species is very close to Perigastrella indivisa Levinsen, 1916, 

 from the shores of Greenland but differs from it in the oval zooecia 

 (and not hexagonal), in the absence of an oral mucron, in the presence 

 of four spines (and not six), and in the development of a peristomie. 

 The latter is much less developed than in Perigastrella labiata Boeck 

 (Smitt, 1867). Our specimens were dead. 



