368 



REVISION OF THE MONAXONlD SPONGES, 11, 



entire length except for a distance of about 5/a (or less) through 

 which they taper to a sharp point; proceeding towards the basal 

 end, however, they usually undergo a slight contraction, and then 

 usually expand again, though only very slightly, at their extremity. 

 Their length, which very rarely falls below 

 160 /x, may attain to 215 /x, and, on the 

 average, is nearer to the latter figure than to 

 the former ; the diameter of the stoutest 

 \ \\ is 6 /i,. 



(6) The tylota are straight or nearly so, 

 with cylindrical or slightly fusiform shaft, 

 and with elongate narrow heads, the ex- 

 tremities of which are truncate, and provided 

 with about a dozen spines, averaging, say, 

 2 /x long; they range between 190 and 240/x, 

 and are seldom less than 210 /x in length, 

 while their diameter is rarely, if ever, more 

 than 3" 5 /x. 



(c)The raphides (onychetse) are straight, 

 asymmetrically fusiform, stylote, tapering 

 gradually to a tine point at one end and to 

 a truncated extremity at the other; their 

 region of maximum stoutness lies nearer to 

 the latter or basal end. Their base is fre- 

 quently rendered apiculate by a minute spine 



^^^•^^- situated at its edge, i.e., outside the line of 



T. diqitata var. ruhi- . . • e ,^ ^^ 



' o. 1- I. continuation ot the axis or the spicule; some- 



cunda. a, otyli. n, . 



Tylota. (Onychela; times there appear to be two such spines, 

 not figured ; similar The basal moiety (only) of the spicule is 

 in spinulation to covered with minute spinules, which decrease 



^° ^ ° * ^ in size towards the middle of the spicule and, 

 var. rubra). . n • 



gradually becoming indistinct, finally give 



place to a scarcely more than perceptible roughness of the 

 surface. The raphides are, at most, 1 -8 /x in diameter, and vary 

 in length from 35 to 130/x; individuals of length between 60 

 and 90 /x, however, are rare, thus indicating a partial differentia- 

 tion of the spicules into two groups. The smaller raphides are 



