490 



DR F. A. BATHER. 



arrangement of the granules is more pronounced in Gl89 (PI. VI. fig. 79), and the 

 ridges are fainter. The doublure on the anal face bears rather coarser granules, in 

 close-set ridges parallel to the border (PI. VI. fig. 76). 



§ 548. Of the Stem some 29 mm. are preserved in the holotype (PL VI. fig. 79), and 

 lie in an almost straight line. At the proximal end the diameter is 37 mm. ; at 6 mm. 

 from the stem-facet the diameter is reduced to 2 mm., and within that space are eight 

 flanges. The intermediate columnals cannot be detected. In the ensuing distal region 

 the stem tapers gradually to a diameter of 1'25 mm. at the broken extremity. At the 

 same time the columnals increase in height, at first rapidly and then more slowly, till 

 the last complete one has a height of 3 "5 mm. In this region the first five columnals 

 show some trace of alternation and of distinction between flanged and intermediate 

 ossicles, but in the succeedino; seven no diff"erence can be observed. 



§ 549. In the proximal region the granules on the flanges form distinct vertical 

 series. In the distal region the transverse banding of the granules over the whole 

 surface is more obvious, but the tendency to vertical seriation is at intervals intensified 

 by slight vertical folds. 



§ 550. Comparison with other Species. — The relations of P. foriolus to P. gibha 

 have already been discussed (§ 534). It has also been stated that some specimens 

 doubtfully referred to P. quadrata might belong to this species (§ 519). When the 

 features can be seen, however, a distinction may be found in the shape of the pectini- 

 rhombs, their more clear-cut border in P. foriolus, and the minute periproctals of 

 this species. 



Key to the Species of Pleurocystis. 



§ 551. Owing to the insufficiency of our knowledge, the construction of a Key on 

 the usual dichotomous plan is not feasible. The following tabular statements will, how- 

 ever, be of some practical use in determination : — 



Plates 

 12 & 14. 



Ehomb 

 10-14. 



Rhomb 

 10-14. 



Rhomb 

 11-12. 



Rhomb 

 1-5. 



Periproctals, 



Average 



Diameter. 



Thecal 

 Outline. 







elongate 



lanceolate 



elongate 

 lanceolate 



elongate 



2-7 mm. 



elongate 

 pyriform 



filitexta 





5) 



)j 



)> 



)) 



1 



broad 

 subovate 



anticostensis 



a 

 < 



)> 



rhomboid 



elongate 



Avidened 



smaller than 

 filitexta 



subquadrate 



elegans 



be 



widened 



lozenge 



wide lozenge 



widened 



1 mm. 



subquadrate 



squaiiiosa 



4 



)» 



sub- 

 triangular 



wide sub- 

 triangular 



? 



1 " large " 



? 



exornata 





>) 



elliptical 



wide 

 elliptical 



widened 



? " minute " 



subovate 



mercerensis 



