GEODIA MESOTRIAENELLA. 151 



coast of North America and coast of Ceylon (Gulf of Manaar), are so far apart, 

 I think it advisable to keep them systematically distinct. 



Geodia (Cydonium) mulleri Fleming, to which species Lambe (loc. cit.) 

 assigned the specimen of G. agassizii examined by him, differs from this species 

 in having much larger and more elongated sterrasters. 



Geodia mesotriaenella, sp. nov. 

 Plate 34, figs. 18-26; Plate 35, figs. 28-35. 



I establish this species for a specimen captured off the coast of southern 

 California at Station 4417. It is similar to the species described as Geodia meso- 

 triaena, but in regard to the size of the body and the dimensions of its spicules 

 is much smaller and to this the name refers. 



Shape and size. The sponge (Plate 34, fig. 19) is nearly spherical; its small- 

 est and largest diameters are 15 and 19 mm. respectively. The surface is 

 quite smooth and covered by a spicule-fur still fairl)^ intact in several places, 

 chiefly near the base. There are no larger oscules. 



The colour, in spirit, is dirty white, rather darker above than below. 



The superficial part of the body forms a cortex composed of three layers: 

 a dermal (outer) laj'er free from sterrasters, 30-60 /t thick; a mitldle sterraster- 

 armour layer, 320-380 /l thick ; and an inner, fibrous layer, free from sterrasters, 

 120-220 fi thick. 



Canal-system. Apart from a few patches on the upper side, the largest of 

 which is roughly circular and 8 mm. in diameter, the whole of the surface is 

 occupied by groups of afferent pores (Plate 34, fig. 20), about 700 fi in maximum 

 diameter and separated by poreless strips, usually 15-50 pt broad. The pores 

 themselves are oval, 20-80 fi in diameter, and the strands of tissue separating 

 them narrower the larger the pores are. In the efferent areas smaller groups, 

 only 200-500 p. in diameter, containing a smaller number of larger pores, 40-160 /x 

 wide (Plate 34, fig. 25), are met with. 



Skeleton. Radial bundles of megascleres traverse the choanosome and 

 penetrate the cortex ; their distal parts protrude freely beyond the surface and 

 form the spicule-fur. The proximal parts of these bundles in the interior of the 

 choanosome are composed entirely of amphioxes. Distally orthotriaenes, 

 mesoprotriaenes, and anatriaenes are added to the amphioxes. Most of the 

 orthotriaene-cladomes he in the inner layer of the cortex. Anatriaene-cladomes 

 are found in considerable numbei-s, both at this and at a lower level. The spicule- 

 fur is composed of the distal parts of amphioxes, mesoprotriaenes, and anatriaenes. 



