126 OKHAMANDAL MARINE ^OOLOGY REPORT— PART 11 



Genus Psammochela n. g. 



Desmacidonidae with a reticulate skeleton composed of sandy and sometimes 

 partly spicular fibres. Megascleres styli or strongyla or both. Microscleres isochBlse, 

 which may be very minute and with vestigial teeth ; to which sigmata may be added. 



I propose this genus for some interesting sand-sponges from the neighbourhood of 

 Beyt Island, which seem to represent a stage in the regressive evolution of such genera 

 as Phoriospongia and Chondropsis. These two genera have no chelae, and I have hitherto 

 excluded them from the Desmacidonidse, but the occurrence of the vestigial isochelae 

 in Psammochela seems to indicate a probable desmacidonid origin. 



I regard Psammochela elegans n. sp. as the type of the genus. Hentschel's 

 Desmacidon psammodes from S.W. Australia [1911] evidently belongs to the same 

 genus. My own Desmacidon (?) arenifibrosa [1896] and Carter's Dysidea chaliniformis 

 { = Desmacidon (?) chaliniformis Dendy [1896]), may belong to a closely related genus 

 in which the megascleres have been completely suppressed. 



37. Psammochela elegans n. sp. (Plate I., Figs. 6a-6e ; Plate III., Figs. 22a, 

 226). 



Sponge (Figs. 22a, 226) irregular, lamellar or digitate, often running out into long, 

 slender, sometimes bifurcating processes, from 3 to 10 mm. in diameter and up to about 

 90 mm. in length in the specimens before me. Surface irregularly rugose or conulose, 

 but with the intervals between the rugae or conuli spanned over in life by a delicate, 

 translucent, minutely reticulate and finely porous dermal membrane. In formahn 

 specimens (Fig. 226) the dermal membrane has completely disappeared, and the 

 sponge has a curiously eroded appearance, the surface being deeply and irregularly 

 grooved and pitted,the grooves and pits being obviously uncovered subdermal cavities. 

 Vents probably rather small and scattered. 



The main skeleton is a fairly close-meshed but very irregular reticulation of rather 

 slender fibre, composed of sand-grains and proper megascleres in varpng proportions, 

 with no visible spongin ; with numerous megascleres and sand-grains scattered in the 

 soft tissues between the fibres. The dermal skeleton is composed chiefly of very fine, 

 scattered sand-grains, with a more or less pronounced tendency to arrange themselves 

 in a fine-meshed reticulation. 



Spicules. (1) Slender styh (Fig. 6a) ; evenly rounded off at the base, rather 

 abruptly sharp-pointed at the apex, often a little crooked ; size about 0-16 by 0-005 mm., 

 but very variable in thickness (? sometimes becoming strongylote). (2) Tridentate 

 isochelse (Figs. 66, 66') ; fairly robust, with stout, curved shaft ; length about 

 0-024 mm. These are usually scarce. (3) Very minute, C-shaped isochelge (Figs. 

 6c, 6c') ; resembling in side view slender, strongly curved, C-shaped sigmata with 

 slightly enlarged ends ; in front view hke an lotrochota " birotulate," with indications 

 of three vestigial teeth at each end ; length from bend to bend about 0-012 mm. 



