PHRISSOCYSTIS ACULEATA. 187 



carrying curved spathiform spines, and separated by the wide posterior 

 ambulacral areas from the lateral interanibulacral ambital plastrons. 



The coronal plates are distinctly imbricating. The ambulacral plates 

 lap in one direction, the interambulacral in the other, as has been observed 

 by Ludwig 1 and Loven for other Spatangoids (Spatangus, Brissopsis, and 

 Eehinocardium). 



M. de Meijere describes a species of Phrissocystis, 2 but as there are no 

 details figured it is impossible to decide if his species belongs to the genus 

 or not. He speaks of a subanal fasciole. There is no such fasciole in the 

 Panamic species. His description of the coronal plates agrees well with 

 those of Phrissocystis, but he does not speak of the remarkable elongated 

 coronal ambital plates. It must be a mistake to say that the vertex and 

 apical system lie in the middle. From his figure 90, PI. X., it has all the 

 appearance of being anterior ; and surely figure 495, PI. XXIII. , cannot 

 be a peripetalous fasciole of Phrissocystis, as M. de Meijere states in the 

 Explanation of the Plates. 



Phrissocystis aculeata A. Ag. 



Phrissocystis aculeata A. Ag., Bull. M. C. Z. 1898, XXXII, No. 5, p 80, Plate XII, figs. 1 -7. 



Plates 88-90. 



At Station 3366, from a depth of 1067 fathoms, a large number of frag- 

 ments of this species came up in the trawl. Though we did not obtain a 

 single whole specimen, yet the pieces and fragments were sufficiently large 

 and numerous to enable me to reconstruct quite accurately this interesting 

 Spatangoid (Fig. 255). In general appearance this species must have re- 

 sembled Linopneustes and Paleopneustes. The test is covered with large 

 primary radioles arranged in distant clusters on the coronal plates (Pis. 88, 

 figs. 1, 2; 89, figs. 1, 2 ; 90) ; the radioles are of uniform size ; those above 

 the ambitus are sharp, curved, from 30 to 40 mm. in length, with secondary 

 small sharp spines scattered along the shaft. There are but few secondary 

 radioles above the ambitus ; they are more thickly clustered along the 

 ambitus (PI. 88, figs. 1, 2). 



1 Ludwig, Morpholog. Studien, and Loven, Etudes, Tls. XXXV, fig 208; XXXVII, fig. 213; 

 XXXIX, fig. 222. 



2 " Siboga " Echinoidea, p. 198. 



