292 



ERYLUS ROTUNDUS. 



smallest is 52. mm. long. One of them possesses, besides numerous small pores, 

 two larger apertures (oscules) 1.5 and 2 mm. in diameter. The single specimen 

 of var. typica, form C, is irregular, massive, and 34 mm. long. Several short, 

 lobose protuberances arise from it. The surface is perforated by numerous 

 small pores and foreign bodies are attached to parts of it. The single specimen 

 of var. typica, form D, is an elongate mass, attenuated at one end to a digitate 

 process, 5 mm. thick. The total length of the sponge is 44 mm. Small pores 

 are scattered over its surface. 



The single specimen of var. cidaris (Plate 5, fig. 31) is an upright, lobose 

 mass, 67 mm. high. Its largest and smallest horizontal diameters measure 

 57 and 45 mm. respectively. Small irregular grooves are observed on its other- 

 wise smooth, undulating surface. Here and there two adjacent grooves extend 

 for some distance in parallel directions, enclosing a gyriform fold. The surface 

 is perforated by numerous small pores, and a few crusts of symbiotic organisms, 

 but no dead foreign bodies, are attached to it. 



The colour of the interior of these spirit specimens varies from dirty white 

 to light brown, that of the surface is subject to considerable variations. The 

 upper part and the sides of the large specimen of var. megarhahda, form A, are 

 dark purplish brown, the base and the interior being light dirty brown. Where 

 the dark colour of the sides gradually merges into the light colour of the base, 

 numerous whitish spots, marking the position of the — mostly closed — pores, 

 are observed on the surface. The smaller specimen of this form is coloured in 

 the same way, but the light-coloured part of the surface is here relatively more 

 extensive. The single specimen of var. megarhahda, form B, is rather dark 

 purplish gray. 



Three of the specimens of var. typica, form A, are purplish brown above and 

 light dirty brown below ; one is bluish gray. The three specimens of var. typica, 

 form B, are dark purplish black above and much lighter purplish brown below. 

 The single specimen of var. typica, form C, is light purple with a small, consider- 

 ably darker patch. The single specimen of var. typica, form D, is dirty white. 

 The single specimen of var. cidaris is whitish with a large brown patch, in 

 which numerous whitish spots, marking the position of the mostly closed pores, 

 are observed. 



The differences in the degree of pigmentation of these sponges are probably 

 due to differences in the amount of light that fell on their surface during growth. 

 I think that in the specimens not uniform in colour, the upper parts, which were 

 more exposed to the light, became more strongly pigmented than the lower parts, 



