SIDONOPS ANGULATA. 27 



circular pore up to 100 ,« wide (Plate 13, fig. 22). In the massive specimen of 

 var. megana and also in var. microana the efferent pores occupy the upper 

 depressed or flattened side of the sponge. In the other two specimens they 

 appear to be distributed less regularly. As stated above the upper face of the 

 massive specimen of var. megana is covered with wart -like protuberances, une- 

 qual in size and on the average about 1 mm. apart. Many of these warts bear 

 on their summit an efferent ])ore, many however are without an apical aperture. 

 I presume that all these warts are pore-bearing elevations and that on those on 

 which no pore was seen, the pore had been quite closed by excessive contraction 

 of the sphincter surrounding it. In the specimen of var. microana, on the other 

 hand, nearly all the efferent pores seem to be open. In this sponge many of 

 them lie on the level of the surface and are not raised above it. 



Skeleton. Spicule-bundles, extending radially and abutting vertically on 

 the surface, traverse the choanosome. In the interior these bundles are chiefly 

 composed of quite stout amphioxes, to which a few thick styles or branched 

 style-derivates may be added. Towards the surface also plagiotriaenes (in 

 var. megana and var. microana) or orthotriaenes (in var. orOiotriaena), anaclades, 

 and long and slender amphioxes (much more numerous in var. microana than in 

 the other varieties) are added to the stout amphioxes (and styles and style- 

 derivates). In var. microana and var. orthotriaena the cladomes of the plagio- or 

 ortho-triaenes lie on the level of the lower limit of the sterraster-armour layer. 

 In the two specimens of var. megana they are situated a little higher up, within 

 this layer, and entirely enveloped in sterrasters. The anaclades are not numer- 

 ous. Most of them are anatriaenes. In var. microana also anadiaenes are 

 met with. The cladomes of some of the anaclades lie in the inner zone of the 

 cortex ; by far the greater number, however, protrude freely beyond the surface. 

 Some long and slender amphioxes lie altogether within the sponge; numerous 

 spicules of this kind protrude beyond it. Together with the anaclades they 

 form the spicule-fur. In it the slender amphioxes are much more numerous 

 than the anaclades. Some of both the stout choanosomal and the slender 

 chiefly dermal amphioxes, and a few of the teloclade-rhabdomes and clades are 

 angularly bent. 



In the spicule-preparations of var. microana two or three dichotriaenes and 

 some mesoprotriaenes were observed. Since however I failed to find such 

 spicules in situ in the sections, I do not believe that they belong to the sponge. 



The microscleres are smooth oxyasters and oxysphaerasters, spined strongy- 

 losphaerasters and sterrasters. The oxyasters are confined to the choanosome 



