NORTH AMERICAN TORIFER^. PART II. 529 



at intervals into a succession of fan-shaped figures. These appear upon the surface of the 

 species which possess this mode of growth as flat, fan-shaped, or fascicular bundles, with a 

 narrow mesh formed by the thickly set and horizontal secondary fibre. In some species 

 the bundles, growing broader towards the surface, would thus become of enormous size if 

 there was not a secondary system of branching which separates the large ones into two 

 or three smaller bundles. There are none of these, properly speaking, in some other spe- 

 cies, but only closely connected sheets of parallel primary fibres with the usual close net 

 work formed by the approximation of the horizontal secondary fibres ; these lead into the 

 genus Spongelia, between Avhich and this genus no definite and constant differences, appli- 

 cable to all the species without reservation, have been found in the skeleton. 



In all the species I have jet seen, the general system of connecting tissue formed be- 

 tween the bundles by the secondary fibres has a remarkably loose and open texture. Of 

 course there would naturally be a great variation in such a characteristic, but as compared 

 with either Spongelia or Spongia, this portion of the skeleton is very loosely put together, 

 and the mesh is usually either of a very irregular form, or composed of horizontal second- 

 ary fibres united hy an independent series of shorter vertical fibres. The bundles of primary 

 fibres radiate from the interior outwardly, and with the connecting tissue of secondary 

 fibres form a mass of more or less perfect tubes also radiating outwardly, as in Spongelia ; 

 and at intervals horizontal canals are formed which connect these tubes with each other, 

 and are of about the same diameter. 



Stelospongos Maynai'dii Hyatt. 



The t^^pical specimen (PI. xvir, fig. 21) of this species is fistulose, but with very thick 

 walls below; the greatest diameter is about 110 mm., height about 150 mm. The central 

 canal is largest at the opening, which is- about three-quarters of an inch in diameter, and 

 the walls are composed of enormous bundles of primary fibres, which sometimes attain a 

 thickness of 7 mm., though generally not more than half that in diameter. The bundles 

 are irregularly rounded fasces of primary fibres, bound together by short, thick, secondary 

 fibres, so closely arranged in parts tliat the intermediate spaces appear like the rounded 

 holes in a sieve, or cullender, while in other parts of the same bundle they may be so 

 wide apart that they resemble more nearly the square spaces between the rounds of a 

 ladder. The primary fibres are always very thick, closely set, and often branch at intervals. 

 This latter characteristic causes a constant increase in the thickness of the bundle, and 

 these would soon attain an unwieldy size if they did not, as they grow outwards, again 

 divide at intervals into two or three diverging fasces. All of these are bound together by 

 a net work of secondary fibres, much coarser than those connecting the primary fibres 

 inside of the bundles, and the mesh is exceedingly large and loosely looped up between 

 them. This connecting system and the bundles of fibres together, form the wall of an 

 unusually regular system of tubes leading into the central fistular cavity. The external 

 openings of these are thickly set, and may vary from 7 mm. in diameter to half that size. 

 The surface of the skeleton is excessively rough, on account of the great size of the fibres 

 and bundles, the number and size of the orifices and the loose arrangement of the con- 

 necting fibres. Perhaps this is even more to be attributed to the irregularity caused by 

 a system of very deep channels connecting all the smaller orifices. These break up the 

 surface and give the bundles the aspect of standing out very prominently from the surface, 



MEMOIRS BOST. SOC. NAT. HIST. VOL. II. 133 



