MR. S. O. RIDLEY ON THE GENUS DIRRHOPALUM. 485 



fucus above mentioned, occur in the Museum collection. It is 

 doubtful whether they were naturally upright in growth, and 

 whether they ever were rooted. The nearest described ally is 

 apparently D. gymnazon, but the generally smaller size of the 

 spicules distinguishes it ; it is also near D. manaarense from 

 Ceylon (v. supra). 



Systematic position o/'Dirrhopalum. 

 Prof. Sollas has already made the genus the type and sole occu- 

 pant of a new " group " named Plocamlanina. I am inclined 

 to think that in so doing he has exaggerated the distinctness of 

 the genus, and that Glathria, Schmidt (as based on G. coralloides, 

 Schmidt, &c), might with advantage be included in the group. 

 The spiculation of the type species of that genus, as shown by the 

 mounting in the British Museum, much resembles that of Dirrho- 

 palum, consisting of a short cylindrical, two sizes of acuates (one 

 of which is contracted at the base), a fine spinulate, and a navi- 

 cular equianchorate ; it has a well-marked horny fibre of distinctly 

 echinonematous structure. More I cannot add from Schmidt's 

 description ; but in support of my view I would bring forward 

 GlatTiria rectangulosa, Schmidt, and the species which, in my 

 view, should be termed Glathria Beani, viz. Isodictya JBeanii, 

 Bowerbank, Mon. Brit. Spong. ii. p. 334, iii. pi. lviii. figs. 1-6.' 



Glathria rectangulosa has small acuate spicules tapering to their 

 base, smooth cylindricals, subspinulate acuates, delicate equi- 

 ancho rates and tricurvates. 



The British G. Beani, Bowerbank, agrees in the most extra- 

 ordinary manner with Dirrhopalum coriaceum in the structure of 

 its skeleton, and also in almost every particular of the forms and 

 distribution of its spicules. It has a primary fibre composed of 

 (1) large smooth acuate, surrounded by a group of (2) smaller 

 ones, which are basally constricted ; and a secondary fibre com- 

 posed of (3) short, thick, entirely spined acuates, basally inflated, 

 of almost the same diameter from the base to within a diameter 

 of the point which abruptly terminates it. There are also a fine 

 tricurvate and an equianchorate flesh-spicule. The spined acuate 

 or spinulate (3) differs from the correspondingly placed dumbbell 

 form of D. coriaceum by the addition of a point to one end, and by 

 the absence, as a rule, of a well-marked head or swelling at the 

 distal end ; this end, however, is frequently marked off from the 

 rest of the shaft by a slight neck, as if to form an incipient head, 



