128 THE VOYAGE OF H.M.S. CHALLENGEE. 



Genus 2. Trachycaulus, u. gen. 

 Only one species is referred to this genus. 



Trachycauhis guiiittii, n. sp. (PI. XXVI. figs. 4-9). 



In the middle of the southern part of the Pacific (Station 289, lat. 39° 41' S., long. 

 131° 23' W.) there was trawled from a depth of 2550 fathoms and a red clay ground, 

 the round stalk — 12 cm. in length and 2 to 3 mm. in diameter — which is figured in 

 PI. XXVI. fig. 4. At the lower thinner end this stalk is slightly bent ; it is otherwise 

 straight, and is at the ujiper end broken across transversely. The surface of this hollow 

 and tolerably firm stalk is covered with hairs. Although nothing remains of the sponge 

 body belonging to the stalk, I cannot doubt from the structure of the fairly well-preserved 

 dermal skeleton that we have to deal with a form closely related to the genus Ccmlo- 

 phaciis. Nevertheless the presence of a very peculiar rosette, and the absence of a form 

 characteristic of the two known species of Caulophacus, even in the stalk, namely, of 

 the frequent dispersalia, pronged discohexacts and discohexasters, prevent one from 

 referring this specimen to that genus. 



Greatly prolonged rod-like smooth diacts with rounded rough extremities form a firm 

 lattice or ladder-like framework for the parenchyma, being bound together in parallel 

 longitudinal rows by means of numerous transverse synapticula. Slender regular 

 hexacts with smooth pointed rays occur in very various positions in the parenchyma, 

 partly as integral parts of the lattice-work, partly only in external connection with it, or 

 else quite freely on its surface. 



Especially remarkable, however, on account of their size ( = 0'4 mm. in diameter) and 

 singular form are the rosettes with short principal rays, upon each of which four long 

 sickle-like terminal rays are placed. These forms occur scattered in the subdermal spaces 

 between the hexacts which have just been mentioned (PI. XXVI. figs. 7, 8). They 

 recall the sickle rosettes of Oscar Schmidt. The inner portion of each terminal ray is 

 very thin ; outwardly the ray becomes graduall}^ thicker, and bears on its extremity a 

 more or less sharply hooked curve finally terminating in a backward bent point. 

 Great variations occur in the form and size of this hook-shaped terminal portion which is 

 sometimes quite irregularly bent, or else divided into two or three diverging points. • 

 Occasionally the four hooks which bend towards one another may fuse together. 



There is a striking agreement between these forms and the " sickle rosettes " found 

 by Oscar Schmidt in his Hcrtwigia falcifera, and figured by him in his Spongien des 

 Meerbusens von Mexico, Taf vi. fig. 8. 



The dermal skeleton is composed of greatly prolonged hexact autodermal pinuli, in 

 which the four transverse rays and the almost equally long proximal ray are simple. 



