16 



PALEOPNEUSTES CRISTATUS. 



gins ; minute distant miliaries arc irregularly scattered between them, and 

 extend over the whole test ; the abactinal tubei'cles arc larger and some- 

 what more crowded in the interambulacral spaces adjoining the petaloid 

 jjortion of the lateral ambulacra. In the odd anilndacrum these large tuber- 

 cles are limited to the abactinal part of the interanibulacrum, where they are 

 closely crowded together, and, carrying, as they do, larger spines, form a sort 

 of tuft near the abactinal pole. The larger spines adjoining the petals protect 

 them, somewhat as in other Spatangoids, by arching over them. The remain- 

 ing spines of the abactinal surface are finely serrated, short, straight, resem- 

 bling at first sight the spines of the regular Echini {Fig. s). They stand 

 out in all possible directions from the test, and have not a general trend, as 

 is the case in all Spatangoids. The spines of the actinal side are somewhat 

 curved, much longer, spoon-shaped at the tip, finely striated, but not serrated 

 [Fif/. o), except near the ambitus, where the spines become straighter and 

 shorter. The spines of the actinal surface trend all in one direction. A 

 transverse section of one of the actinal spines {Firj. lo) shows the general 

 structure of Spatangoid spines. The large open cells of the central portion 

 of the shaft, characteristic of these spines, are not a common feature among 



Fio. 8. 



Fig. 9. 



Fig. 10. 



Fig. 12. 



Fig. 11. 



Spatangoids, where the central space is generally hollow ; these large cells 

 recall the structure of the central part of the spine in Diadematidae and in 

 Arbaciadae. The miliaries carry minute silk-like spines of similar structure 

 with the larger ones ; and either large pcdicellaria?, Avith rather stout stems 

 {F/ff. n) and large heads {Fig. 12), similar to those of Spatangus proper, or 



