G6 SILICEOUS SPOXGES. 



1877. Siphonia Konigii, SoUas, Quart. Journ. Geol. Soc. vol. xsxiii. p. 817. 



1878. Siphonia Koenigi, Zitt. Stud. II Ab. p. 79. 



Sponges pear-shaped or subsplierical, the summits usually truncate ; stem cylin- 

 drical, apparently slender. An average specimen is 100 mm. in height by 70 mm. 

 in width. 



The cloacal tube is cylindrical or funnel-shaped, and extends nearly to the basal 

 portion of the body. Its apertui'e is very wide, and the margins are rounded. Very 

 strongly marked branching canals, 2 mm. in width, radiate from the margin of the 

 cloaca down the sides of tlie sponge. The lateral surfaces exhibit circular or sub- 

 angular apertures of canals from 1 to 2 mm. in width. Some of these apertures are 

 bridged over by minute thread-like extensions of spicular fibre crossing them. 



The spicules forming the mesh are relatively large, but they are so incrusted with 

 silica that it is impracticable to measure them. A dermal layer appears to have 

 extended over the outer surface of the sponge and over the interior of the cloacal 

 tube as well. The spicules composing it have horizontally expanded, slightly bifur- 

 cate head-rays ; the shafts, if present, extended into the sponge. 



Most of the examples of this species are preserved in the interior of flints, and 

 retain merely the form of the cloaca and the larger canals, the spicular structure 

 having entirely disappeared. There are, however, in the Museum collection a few 

 specimens from Flamborough which, in common with the other sponges from that 

 locality, are preserved in a chalky matrix, which can be removed by treatment with 

 dilute acid ; and these exhibit the form and canal-structure in a very perfect manner, 

 but the spicules for the most part are masked by siliceous accretions. They further 

 show the important feature of a dermal layer, which has hitherto not been discovered 

 in any example of the genus. This layer covered over the exterior branching summit 

 canals, and seems also to have covered the interior surface of the cloaca, for in a 

 well-preserved specimen the cloaca exhibits a smooth surface like that of the exterior, 

 and here and there the openings of the canals can be detected beneath this layer. 



In some of the examples of this species, preserved in flint, there is a filled-up 

 spiral tube or canal, from 4 to 8 mm. in width, which winds through the interior of 

 the body between the cloaca and tlie outer surface, and opens out at the summit of 

 the sponge in the vicinity of the cloacal aperture. This tube has been described by 

 Cunnington * as forming part of the original fabric of the sponge, and probably 

 connected with the reproductive system. The more probable suggestion is that the 

 tube has been formed by an annelid, which has built its shell 'pari passu with the 

 growth of the sponge ; and it is not improbable that its constant proximity to the 

 cloacal aperture has arisen from the support which the animal inhabiting the tube 

 may have derived from the stream of water passing out of the cloaca. Examples in 

 the Museum show clearly that this spiral tube was not peculiar to this species of 

 * Kcport of British Association, Swansea, 1848, p. 67. 



