86 PANAMIC DEEP SEA ECHINI. 



or among those of Hygrosoma available for comparison showing reasons 

 for the adoption of Hygrosoma as contrasted to Phormosoma. 



It is with a sigh of relief that Dr. Mortensen^ comes to Fh. asterias, '-'the 

 last of the Echinothurids described from the 'Challenger'"; to be exact I 

 beg to call his attention to the fact that it is not the last species described. 

 Of course he finds the description useless. Fortunately some of the 

 figures meet his approval, and a new genus is established for the species 

 based on characters which to me appear most trivial. 



Phormosoma Wyv. Thom. 



Phormosoma hispidum, A. Ag. 



Phormosoma hispidum, A. Ag., Bull. :M. C. Z. 1898, XXXII, No. 5, p. 77. Plates VI, VII. 



Plates A; B, fig. 1; 30-42; 43, figs. 5, 6'; 44-47; 48, figs. >^-6; 49. 



This species is the Pacific representative of the Caribbean and Northern 

 Atlantic Ph. uranus. It has like it an extensive geographical distribution 

 from the Panamic to the South Californian district, but in comparatively 

 dee])er water. Its range is from about 1000 to over 1300 fathoms, while 

 the Atlantic species has been found at a much less depth (309 fathoms). 

 An excellent series of specimens of this species was collected, varying from 

 15 mm. to 203 mm. in diameter (Pis. 30-38), the greater number being from 

 120 to 130 mm. in diameter (Pis. 31, fig. ;?; 32; 33, fig. J; 34, fig. i; 

 35; 36). In the largest specimen, 203 mm. in diameter (Pis. 37; 38) the 

 actinal system was 44 nun. in diameter (PI. 41, fig. 2) and the apical 44 mm. 

 (PI. 39, fig. 3). The test is marked by the great widtli of the ambulacral 

 system, which at the ambitus is no less than 57 mm., — nearly of the same 

 width as the interambulacral area at the corresponding edge. 



It will be simplei' to describe first the 3'oungest specimens collected, and 

 trace the changes taking place with increasing size, until we reach the 

 larfil-est specimens dredged by us. 



The young st.ages of Phormosoma are less globular, more flattened, like 

 Diadeina, (iian the older stages (PI. 30). The youngest specimen collected 

 (PI. 30, figs, y, '2) measured 15 mm. in diameter. Fig. 133 ; the actinal 

 system 5 mm. in diameter (Pis. 43. fig. 5\ 44, fig. i; 48, fig. 2). with three 



* " Ingoif " Echiuoidea, p. CO. 



