46 



SIDONOPS BICOLOR. 



chip of an adult sterraster, which I was able with a high power to photograph 

 (Plate 8, fig. 12). This photograph shows that the centre of this spicule is 

 occupied by a cluster of granules (a), from which the radial lines, traversing the 

 body of the sterraster, arise. The central granule-cluster is about 4 in 

 diameter. 



The rays protruding over the surface of the solid centrum are in most of 

 the adult sterrasters (Plate 8, figs. 10, 11) 2-3 n thick and provided with terminal 

 verticils of usually five or six lateral spines. In some of the sterrasters (Plate 

 8, figs. 6-8) these rays are 3.5-4.5 n thick and usually provided with seven 

 or eight lateral and one or more obliquely arising terminal spines. 



Both specimens were collected on April 13, 1888, at Duncan Island, Gala- 

 pagos. They were labeled F. C. 1354 and 539 Tetractinellida. 



The structure of the skeleton, the cribriporal afferents, and the uniporal 

 efferents show that this species belongs to Sidonops. It is not at all closely 

 allied to any other species of Sidonops or to any species of Geodia. The species 

 approaching it most closely appears to be Geodia media Bowerbank from which 

 however it differs by the small euasters for the most part being thick- and 

 short-rayed strongylosphaerasters and by the presence of mesomonaenes. 



Sidonops bicolor, sp. nov. 

 » ^ Plate 9, figs. 1-19; Plate 10, figs. 1-15; Plate 11, figs. 1-17. 



" <f'y2.o " % 37^7 ^ establish this species for fifteen specimens obtained off California. All 



M 5" 5 / " « H "T) the specimens agree closely and most of them are very much lighter in colour on 

 '/ X'^ s'ir ,< ^ ty 0 / (1) one side than on the other. The specific name, bicolor, refers to this conspicuous 

 M53( , i^o^i^) character. 



Shape and size. These sponges are irregularly tuberous, and generally 

 considerably elongated (Plate 11, figs. 15, 16) or flattened (Plate 11, fig. 17). 

 The largest elongated one, which was obtained at Station 2958, is 101 mm. long 

 and 40 mm. thick. The largest flattened one, collected at Station 2981, is 62 

 mm. long, 59 mm. broad, and 28 mm. thick. The others are 39-73 mm. in maxi- 

 mum diameter. Most of the efferent pores are situated on the less extensive 

 concave parts of the surface, while the afferents are chiefly on the more extensive 

 convex parts. The areas bearing chiefly the efferent pores are either quite 

 smooth or slightly raised around these pores, some of which are situated on the 

 summits of low elevations. The areas bearing chiefly the afferent pores are 

 more uneven and appear to have been entirely covered with a spicule-fur. 

 Although rubbed off in many places, remnants of this spicule-fur can easily be 



