REPORT ON THE HEXACTINELLIDA. 211 



is a small flat tubercle-like process, representing the abortive sixth ray. The lono- stalk 

 exhibits, like the four anchor teeth, a distinct axial canal. 



Subgenus 2. Stylocalyx, n. subgen. (PI. XXXI.; PI. XXXIV. figs. 1-11; 

 Pis. XXXV., XXXVIL, XXXVIIL, XL., XLL). 



The superior aperture of the gastral cavity is not covered by a sieve-plate, but 

 remains quite open. The gastral cavity is divided into four chambers by a central cone 

 and four cruciate radial septa. 



1. Hyalonema {Stylocalyx) thomsoni, Marshall (PI. XXXIV. figs 1-11). 



In his memoir on the HexactineUidre^ W. Marshall describes a species of Hyalonema 

 obtained by WyviUe Thomson on the "Porcupine" Expedition to the north of the Shetland 

 Islands, at a depth of 550 fathoms. This form measured 7 cm. in length, 3 "5 being 

 occupied by the body proper, and 3 "5 by the basal tuft, and about 8 mm. in thickness. 

 Through the kindness of 0. Schmidt I have been able to examine this di-ied specimen. 

 The body ^ has a spindle-like form, the upper end not being transversely truncated, 

 but extending to a somewhat pointed apex, in the form of a projecting cone. The 

 basal tuft is surrounded, just below the lower pointed end, by an encrustation of 

 Palythoa, 3 mm. in length, and with four or five polypes. The number of 

 slightly twisted basal spicules is estimated by Marshall at fifty or sixty. On some 

 of them he observed a ridge with nail-like teeth, which was absent from others; the 

 lower ends are all broken off. In the still partially preserved external dermal 

 skeleton Marshall found regular "four-rayed" spicules which were mutually apposed 

 by their limbs, and also several five-rayed forms. In the fir-tree forms situated on these 

 spicules of the dermal network the spinose principal ray projects, according to Marshall, 

 into the lumen of the rectangular dermal meshes in the plane of the skin, that is, lies 

 tangentially. Besides these, amphidiscs occasionally occur, 0"03 to 0'08 mm. in length, 

 and with six long, narrow, pointed anchor-teeth, as well as very small (O'OOB mm. in length) 

 double anchors. Within the body of Hyalonema thomsoni, Marshall describes fom- 

 large cavities, into which large and small parenchymal passages open. On the wall of 

 these cavities long curved uniaxial spicules occur, besides isolated smooth six-rayed forms 

 and amphidiscs with small double anchors. In the parench}Tiia proper he found, 

 besides the long uniaxial spicules, four-, five-, and six-rayed forms, and most frequently 

 small hexacts. 



In the covering membrane, which extends from the truncated superior and external 

 margin to the conical knob projecting freely in the centre, Marshall observed four cleft- 



1 Zeitschr.f. leiss. Zool., Suppl.-BJ. xxv. p. 225, 1875. '^ Loc. cit., Taf. xvii fig. 84. 



