POEOCIDARIS COBOSI. 29 



Porocidaris Cobosi A. Ag. 



Porocidaris Cobosi A. Ag. Bull. M. C. Z., 1898, XXXII, No. 5, p. 74, Plate III, figs. 2-5. 



Plates 9; 10, figs. 4.-9; 11; 12; 13, figs. 1-4. 



This species is characterized by its small actinal and abactinal systems 

 (PL 9, fig. 4), its stout primary radioles (PI. 9, figs. 1-3); the primary 

 tubercles are perforate and crenulate (PI. 10, figs. 6-9) in older specimens, 

 but are not crenulate in a specimen 8 mm. in diameter (PI. 10, figs. J,, 5). In 

 the largest specimen examined, a female 35 mm. in diameter (PI. 11, fig. 6), 

 the abactinal system is only 14 mm. in diameter. The genital plates are quite 

 regular in outline compared with those of P. Millm, and they as well as 

 the ocular plates are covered by larger, coarser, and more distant secondary 

 tubercles, with still fewer miliaries than in that species. In a younger 

 specimen, a male 21 mm. in diameter, the secondaries on the genitals are 

 reduced to a single row of three on the anal edge of the plates and to 

 two or three miliaries in the centre of the distal part; on the oculars 

 an arc of four or five miliaries is found round the ocular pore (PI. 11 

 fig. 5). In this specimen the anal system is isolated from the oculars, 

 and the larger of the anal plates carry a miliary. In the larger specimen 

 the anal system reaches the right posterior ambulacrum, and the larger 

 anal plates carry from two to four secondaries and miliaries. The genital 

 plates of this species are more elongate than in I'. Milleri, and the ocular 

 plates are much larger. Compare Pis. 11, figs. 5, 6; 12, fig. 1, with PI. 7, 

 figs. 1-5. 



Plate 12, fig. S, shows, seen from the inside, the abactinal plates of the 

 right posterior ambulacrum, with the newly formed ambulacral plate 

 adjoining the ocidar plate. The ocular pore is, as is seen in Pis. 11, figs, 5, 

 G ; 12, fig. S, placed at a considerable distance from the ambulacral edge of 

 the plate. 



In older specimens we find the usual difference in the size of the 

 genital openings of the males (PI. 11, fig. o) and females (PI. 11, fig. 6). 



In the youngest specimen found. 8 mm. (PI. 12, fig. i), the genital open- 

 ings are covered by lamella> forming wart-like protuberances (PI. 12, figs. 

 9, 10), and the granulation of the abactinal plates is reduced to two to four 

 miliaries on the genitals and to two on the oculars. The symmetrical out- 

 line of the plates of the abactinal system is well seen in this young specimen. 



