44 R. KIRKPATRICK. 



HOPLAKITHARA Kirkpatrick.* 

 1907. HnplakUhara Kirkpatrick (10a. p. 285). 



Mycalinae possessing exotyles with large spherical spined heads, and with fim- 

 briated placocheles. 



HOPLAKITHARA DENDYI. 



(Plate XIX., figs. 6, Ga, 6b, and Plate XXIII., fig. 6a-c 2 .) 

 1907. Hoplakitliiira dnuliji Kirkpatrick (10a. p. 286). 



Sponge in form of a small cushion, attached by a narrow base. Surface smooth 

 to the naked eye. Colour, pale brown in spirit. Consistence, hard externally, soft 

 within. Flagellated chambers 32 * 5 M in diameter, spheroidal, curypylous. 



Skeleton with protective armour formed by gigantic spheroidal heads of exotyles, 

 the exotyles being arranged as radiating bundles in form of inverted cones, with the 

 apices a little below the cortex ; with scattered strongyles. 



Spicules. Megascleres. Exotyles f with the heads a little inclined to the 

 long axis of the spicule, the proximal end (in the interior of the sponge) rounded, the 

 distal end swollen into large spherical heads, with short cylindrical spines covering the 

 distal three-fourths of the head. Total length 358/u, the shaft enlarging in diameter 

 from 6 5 ^ at the proximal end .to 16 M just below the head. Head, 55 /x in diameter ; 

 cylindrical denticles, 1 76 to 3 52 p. in height, with finely denticulate edge, and with 

 cup-like depression at the summit. 



Strongyles straight, fusiform, smooth, 467 ' 5 /u long, 9'75M iu diameter at centre, 

 6 ' 5 M in diameter at ends. 



Microscleres. Placocheles, fimbriated, 84 5 M long, 29 25 p. broad ; length of 

 tooth, 37-75 n. 



Sigmata very small, slender, Q-shaped, 8 8 n long, 5 ' 28 M broad, 9 /j. thick. 



The minute spheroidal or cushion-shaped specimen was 2 2 mm. in height and 

 3 mm. in horizontal diameter ; it was growing on the side of an Alcyonarian, creeping- 

 over a branched Cellepora. No pores or oscules were discernible. The under surface, 

 which was narrowed to the point of attachment, was paler in colour than the upper. 



The new genus is closely related to the Mycaline genera Rhaphidotheca and 

 Guitarra, to the former by its exotyles, and to the latter by its fimbriated placocheles. 



The distal knobs of the exotyles of E. marshall-hallii Kent, 49 M in diameter, are 

 smooth and spherical, and those of 7?. rhopalophora Schmidt (/?. affinis Carter, s^Thiele 

 22. p. 383) are 104 n long and 30 /u broad and club-shaped. Lundbeck (13. p. 32) 

 regards these two species as probably identical, and certainly the differences are slight. 



In the centre of the heads of the exotyles of //. dendyi is an oval granular zone, 

 which at first suggests a cavity filled with protoplasm, but that there is no cavity is 



* oTrXn (pi. of u7rXm<), armour; Kidupn, a guitar. 



t 1'rot'essor ]>fndy. to whom I showed these remarkable exotyles with their large spined heads, regarded them 

 as possible examples of spieules which might form a surface layer of pseudasters by reduction of the shafts. 



