PHEISSOCTSTIS ACULEATA. 189 



The primary interambulacral tubercles increase gradually in number 

 from the apex towards the ambitus, there are at first one or two to three 

 or four, the intertubercular spaces being filled with secondaries (PI. 88, 

 figs. 1, 2). The secondaries also increase in number with the primaries, but 

 on the whole the interambulacral coronal plates above t lie ambitus are 

 comparatively bare, the tuberculation occupying but a part of the central 

 area of the plates. 



In the odd interambulacrum a slight median furrow extends from the 

 apex towards the ambitus to the anal system. The plates of the odd inter- 

 ambulacrum (PI. 90, figs. 7, 4), except those near the apex, carry a larger 

 number of primaries, from six to ten, than those of the lateral interambu- 

 lacra. they are also closely clustered in the central part of the plates, and 

 towards the anal system (Pis. 88, fig. 5 ; '.Ml, fig. S). The whole test is cov- 

 ered with minute distant miliaries scattered irregularly over the coronal 

 plates (Pis. 88-90)." 



The anal system is irregularly circular (PI. 90, fig. .,'), covered with 

 elongated polygonal plates gradually decreasing in size from the outer edge 

 of the anal system to the anal opening; each plate carries a few small milia- 

 ries. The anal system is on the truncated edge of the ambitus (PI. 88, 

 fig.-"); it is circular, covered with small polygonal plates.' The ambitus 

 makes a sharp angle with the floor of the actinal surface, and, owing prob- 

 ably to the pressure from the actinal and abactinal sides, both the inter- 

 ambulacral and ambulacral plates become very greatly elongated (Pis. 88, 

 figs. J, ,.', 3, 5 ; 90, figs. .], 4), five to six of these long narrow ambital plates 

 occupying no greater height than that of a single plate above the ambitus 

 (PI. 88, figs. 1, .', 5), much as in Linopneustes. 



In one of the larger fragments the phyllodes are greatly developed. 

 There are six or seven pairs of pores in the anterior lateral ambulacra. 



It is difficult to determine from the fragments the exact shape of the acti- 

 nal plastron, it may be like that of Linopneustes and have a long slender 

 labium, or a short labium (PI. 88, fig. 4) more like that of Paleopneustes. 



This species is marked by the great width of the posterior interambulacral 

 area at the ambitus (PI. 88, fig. l). The outline of the test seen from above 

 must have been much like that of Linopneustes, only with a more angular 

 outline (Fig. 255) at the ambitus, owing to the re-entering angles in the 

 median interambulacral area at the ambitus (PI. 88, figs. 1, ;J). 

 i Bull. M. C. Z. XXXII, No. 5, PI. XII, fig. 6. 



