TETRAXONIDA 291 



/. pauper a is encrusting, with inconspicuous oscules; colour (dried) "light ochreous 

 yellow". 



/. gracilis is ramose and branching, with small oscules ; colour (alive) pale buff, (dried) 

 cream white. 



/. imitata is encrusting, with no visible oscules ; colour (dried) " brown with tint of 

 green". 



/. dubia is encrusting, with no conspicuous oscules; colour (dried) "light grey with 

 tint of yellow", (alive) orange. 



/. hispida is encrusting, with no visible oscules ; colour (dried) dark grey. 



/. nodosa is massive, with fistulous oscules; colour (dried) light brown. 



/. involuta is encrusting, with no apparent oscules ; colour (dried) dark brown. 



/. scittda is encrusting, with no apparent oscules; colour (dried) "light ochreous 

 yellow". 



With the exception of /. gracilis, there is nothing in the shape of these sponges to 

 justify a segregation into different species. The colour records taken from the dried 

 state may be ignored. In my experience, the result of drying, so far as colour is con- 

 cerned, depends more on the manner in which the sponge is dried, than on the colour 

 in the living condition. The records taken from living specimens show considerable 

 variation in colour, but with a tendency to a reddish tint. 



If any division is to be made it must take the form of separating the twelve species 

 into two forms of a single species, a branching form, including /. gracilis, and a massive 

 form including all the rest. Even so, it is probable that the two forms are purely eco- 

 logical and that in the course of future investigations, all gradations between the two 

 may be found. 



The dimensions of the spicules of Amphilectus fucoriim, as exemplified by the holo- 

 types of the twelve species of Isodictya enumerated by Bowerbank, are: oxea 0-13 5-0-2 

 by o-oo3-o-oo8 mm., and isochelae o-oi4~o-oi8 mm. 



Gray {loc. cit.), Vosmaer {loc. cit.) and Topsent {loc. cit.) add nothing new to our 

 knowledge of these forms. Ridley (1883) described two specimens from Scotland, under 

 Amphilectus edwardii, one of which was erect and branching and the other cylindrical. 

 At the same time, he doubts the identity of Isodictya gracilis with I. edwardii, although 

 his own specimens had the external form of the former. On the other hand, Levinsen 

 {loc. cit.), Lundbeck {loc. cit.) and Stephens (1921) leave no doubt that Esperiopsis 

 fucorum may be either encrusting or branched. Further, I have seen massive speci- 

 mens from Plymouth, with large oscules, in which the surfaces were beset with 

 numerous blunt processes, up to 2 cm. long, undoubtedly representing incipient 

 branches. We may now assume, I think, that there is nothing peculiar about Isodictya 

 gracilis and that it is a synonym of Amphilectus fucorum. 



Numerous specimens of Amphilectus fucorum have been recorded, under various 

 names, from the southern hemisphere which agree in external form with those of the 

 northern hemisphere. They have this in common, however, that the styH are considerably 

 larger in the southern forms and the chelae slightly so. The recorded measurements of 



