KEPORT ON THE HEXACTINELLIDA. 309 



rangularly based on a hand-like expansion of tlie end of the shaft; a straight large shaft 

 more or less beset with long thorn-like spines, most numerous towards the centre where 

 they are vertical, and at the extremities wdiere they are divergent, each slightly curved 

 and microspined ; and a smaller kind in which the rays are straight smooth and capitate." 



In 1875, in his Classification of the Spongida,^ Carter erected within the famUy of the 

 Vitreohexactinellida a special group — the Scopulifera — in which he noted, as type, 

 Aphrocallistes bocagei, Wright. 



Marshall (1876)" ranked the genus Aphrocallistes in his group of Pleionacidfe, and 

 characterised it in the following words : — " Polyzoic, walls with prismatic anastomosing 

 radial tubes; individuals more or less tubular or ball-shaped, astomate, arranged into 

 groups by partition walls. Framework-tissue possessing an apparent regularity. 

 Spicules do not throughout constitute the groundwork of the siliceous beams. The 

 latter are often strangely bent." 



ZitteP (1877) based his family Mellitionidse on the genera Ajihrocallistes, Gray 

 Fieldingia, Saville Kent, Stauronema, SoUas, and noted the following characters : — 

 "Sponge body branched, spherical or plate-like. Wall completely perforated by 

 numerous tubular water, canals and thus divided into honeycomb-like chambers. 

 Skeletal spicules with thick intersections. Surface (naked 1 or) overspread by a delicate 

 meshed or porous siliceous skin, which also covers the openings of the canals. Root 

 absent." 



Oscar Schmidt found Aphrocallistes abundantly among the sponges of the Gulf of 

 Mexico.^ He believed that the peculiar structure of the six-sided prismatic parietal 

 meshwork could be explained by a modification of the fundamental hexradiate spicules — 

 in which all the six rays do not cross at an angle of 90°, but two at an angle of 120°. He 

 compares the lattice-like retiform transverse walls to the sieve-plate of Eu^ilectella and 

 suggests that they had been formed during pauses in the growth. The shaft provided 

 wdth prongs on both ends and on the middle, which was proposed as a charac- 

 teristic feature of the species Aphrocallistes heatrix, 0. Schmidt declares to be an 

 accidentally intruded element, and expresses the belief that this species is not specifically 

 distinct from Aphrocallistes bocagei. 



During the " Porcupine " Expedition a cup-shaped sponge fragment, 1^ cm. in height, 

 was dredged off the south-west coast of Spain from 1095 fathoms. This formed the 

 swollen base of a Hexactinellid and was carefully described by Duncan in 1881^ as a new 

 species of Ap>hrocallistes. If this sponge belongs to the genus Aphrocallistes — which, 

 however, according to Duncan's description of the continuous skeletal framework, can 



1 Arm. and Mag., Nat. Hist., ger. 4, vol. xvi. p. 199. 



2 Zeitschr. f. vriss. Zool., Bd. xxvii. p. 124. 



3 Studien iiber fossile Spongien, Ahhandl. d. baier. Akad., ii., vol. xxii., div. 1. p. .3G. 

 ' Spongien des Meerbusens von Mexico, 1879-80, p. 48. 



5 Journ. Linn. Soc. Land., vol. xv. pp. 324-328. 



