142 THORECTA. 



Genus THORECTA, n. gen. 



Spongidse with a loose skeleton-net, with meshes 0'5-r2 mihim. 

 wide ; stout, simple or branched connecting-fibres, and a thick 

 sand-cortex on the smooth surface. Without superficially extend- 

 ing oscular tubes and corresponding grooves in the skeleton. 



Thorecta exemplum, n. sp. 



Synonj^ms will be found below in the descriptions of the varieties. 

 In this species I combine some different varieties, which are connected with 

 each other by abundant transition forms. All the sponges belonging to it are 

 erect, attached, with a small base, or pedunculate. T. exemplum, var. prima, 

 is lamellar, flabelliform, curved, with oscula 1*5-3 millim. wide, which are 

 abundant on, and confined to, the concave side of the lamellar sponge. In 

 T. exemplum, var. secunda, which is an elegant cup-shaped form, the margins 

 of the curved lamella of T. exemplum., var. prima, have joined, and the lower 

 part has formed a peduncle. The 2-3 millim. wide oscula are accordingly 

 confined to the inner surface of the cup. A further development in this 

 direction is presented by T. exemplum, var. tertia, a pedunculate, somewhat 

 wedge-shaped sponge, on the upper sux'face of which one large 10-15 millim. 

 wide central and several smaller 1-2 millim. wide scattered oscula are observed. 

 Here the cavity of the cup has been filled up more or less, and nothing is left 

 of it but the large central oscular tube. 



The other variety, T. exemplum, var. marginalis, diverges in a different 

 direction. It is pedunculate, erect, and compressed, more or less flabellar, 

 and the 3-5 millim. wide oscula are situated marginally, in pretty regular 

 rows on the crests of a number of longitudinal, regularly meridional, or more 

 often slightly curved ridges. 



It will be seen from this that in this species some of the frequent variations 

 in the form of sponges are particularly forcibly illustrated, and I have named 

 the species '■'■ exemplum^'' on account of this. 



I have drawn attention to this sponge on account of its variability on a 

 previous occasion *. Since then I have examined a great many other speci- 

 mens, and the views expressed by me with regard to them Qoc. cit.) have been 

 confirmed. 



The surface is, in most of the varieties, even or slightly undulating. Only 

 in T. exemplum, var. tertia, it appears deeply pitted in consequence of the 

 presence of high prominent ridges, which form a network, in the meshes of 



* R. V. Lenclenfeld, " A Monograph of the Horny Sponges.— Part VI. The Genus Eu 

 spoiigia" Proceedings of the Linnean Society of New South Wales, vol. ix. pp. 307, 308 (1885) 



