PALEOPNEUSTES AND LINOPNEUSTES. 



181 



anterior ambulacra! groove, the test is not indented at the ambitus, and 

 above it the anterior ambulacrum is flush with the test, but not slightly 

 petaloid as are the other ambulacra. It would also seem as if in P. cristatus 

 the wide bare posterior lateral ambulacra on the actinal side (PI. 95) were 

 more similar to those of Linopneustes (PI. 92) than to the tuberculated 

 actinal ambulacra of P. hystrix (PI. 97). 



On examining the actinal surface of the specimen of P. cristatus figured 

 on Plate 95, we find the interambulacra of the whole posterior part of the 

 test and a part of the anterior actinal surface covered with the remnants of 

 scrobicular areas of tubercles which once occupied their place and which have 



135 mm. 



Fig. 266. Paleopneustes hystrix. 



110 mm. 

 Fig. 267. Linopneustes i.ongispinus. 



been resorbed. The ambulacra have suffered to the same extent, as can 

 be seen from the empty scrobicular circles of the plates of the anterior 

 lateral ambulacra and from the posterior part of the lateral posterior 

 ambulacra, as well as from the two narrow bands of primary tubercles still 

 remaining unaffected on the two sides of those ambulacra. In P. hystrix 

 we find a few of the same empty scrobicular circles on the actinal surface 

 in both areas, but in this species they are not found to such an extent as to 

 affect the general appearance of the test (PL 97) as they do in P. cristatus 

 (PI. 95), in which, when the primary tuberculation has gone, they cover the 

 actinal surface with bare blotches, more extended and connected on the 



