THOHECTA.. 147 



Geographical Distribution. — Key West (Tale Coller/e Coll.) ; Havana 

 (Museum of Comparative Zoology Coll., Cambridge, Mass.). 



South coast of Australia : Phillip Island, V. {Boston Society Coll.) ; Port 

 Phillip Heads, V. {B. Wilson) ; Western Port, V. {B. Wilson). East coast of 

 Australia : Port Jackson, N. S. W. (Lendenfeld) ; New Zealand (BritisJi 

 Museum Coll.). 



Thorecta exemplum, var. marginalis^ nov. 



Erect, very regularly shaped, often symmetrical-, more or less pedunculate 

 sponges, which attain a height of 150-300 millim. and a width of 30-50 millim. 

 The sponge is compressed, often lamellar; it tapers towards the upper end, 

 and also towards the narrow base or the short peduncle, and accordingly 

 appears more or less fusiform. 



Longitudinal, meridional, or slightly curved ridges are observed projecting 

 from the surface ; these are sometimes, particularly in large specimens, so highly 

 developed that they appear as lamellar structures which may attain a width of 

 30 millim. and a thickness of 6-12 millim. 



The oscula are 4 millim. wide and confined to the crests of these projecting 

 ridges, where they are about as far apart as wide. These oscula-rows extend 

 nearly down to the peduncle. 



Smaller specimens are often very symmetrical, particularly those from the 

 West coast of Australia. A radial quadrilateral symmetry is observed in them. 

 The transverse section appears as an elongate square with projecting corners. 

 This figure is perfectly symmetz'ical, and the same figure is produced by every 

 transverse section, with the exception of those through the regularly cylindrical 

 peduncle. The broad and the narrow sides of this sponge are concave, and the 

 oscula situated in four regular meridional rows on the four meridional crests. 

 They are in these smaller (only 100 millim. high) specimens 3 millim. wide and 

 6 millim. apart. 



The dry skeleton is greyish brown aud very soft. 



The skeleton consists of very knotty main fibres, O'07-O'l millim. thick, 

 which are cored with large sand-grains ; and comparatively much branched 

 connecting-fibres, 0-046 millim. thick, which occasionally form dense trellis-like 

 reticulations in the vicinity of the main fibres. The larger meshes are irregular 

 or square, 1 millim. wide. 



The surface-skeleton consists of bands of sand-grains, 0-7 millim. broad, 

 which form a dense network with more or less circular meshes 0*4 millim. wide. 

 In the perforated membranes, which are spread out in them, spicule-fragmeuts 

 are abundant. 



Geographical Distribution. — Mauritius (Canterbury Museum Coll., Christ- 

 <-hurcJi, N. Z.), 



l2 



