24 PANAMIC DEEP SEA ECHINI. 



Porocidaris Des. 



Studer lias limited the genus Porocidaris and associated with it some 

 fossil species which would eliminate from the genus not only Porocidaris 

 Sharreri, as he suggests, but also the new species of Porocidaris discovered 

 by the " Albatross " off the Panamic coast. Studer inclines to associate 

 P. Sharreri with Pleurocidaris of Pomel, which contains both Jurassic and 

 Tertiary types, with miliaries ai'ranged in horizontal rows separated by 

 fine furrows in the interambulacral area, but with smooth noncrenulated 

 tubercles. 



Tn P. Cobosi the tubercles are crenulated and perforated. In P. Milleri 

 they are smooth and perforated, while the general arrangement of the 

 miliary interambulacral tubercles is the same in both, and does not recall 

 in any way their arrangement in horizontal rows, as in P. Sharreri. In 

 P. elegans the miliaries are irregularly arranged and occupy only a small 

 part of the interambulacral plates, which is nearly all taken up by the 

 scrobicular area of the primary tubercle ; they are more closely packed, 

 and there is but a step from this to the linear arrangement of the miliaries 

 in P. Sharreri, with primary tubercles having a comparatively smaller scro- 

 bicular circle defined by a single row of secondaries rising almost like a 

 ridge round it, 1 which remind us more of such Cidaridae as Chondrocidaris. 



Oppenheim 2 is of the opinion that the recent species of Cidaris referred 

 to Porocidaris by Thomson and myself are hardly to be placed in the 

 genus as originally defined by Desor. 3 While the recent and fossil species 

 both have peculiar toothed spines on the actinal surface, }'et the recent 

 species do not possess the furrowed grooves of the scrobicular area which 

 Desor regarded as characteristic of the genus, the systematic value of 

 which is most problematical. 



On the strength of such slight characters Dr. Mortensen asserts that 

 Porocidaris elegans has no relation to Porocidaris purpurata, and suggests 

 the name of Histocidaris for the reception of Porocidaris elegans. The 

 ground for this it is impossible to conceive, unless it be that the char- 

 acters of a single valve of a small globiferous pedicellaria, which he figures 



1 " Blake " Echini, PL TV. fig. 1. 



2 Oppenheim, P. Revision d. Tertiiiren Echiniden Venetieus u. v. Trentino. Zeitschr. d. 

 deutsch. geol. Ges., 54 (1902), p. 174. 



a 1 >r.--or, .Synopsis, p. 47. 



