SPONGES.-HALLMANN. 



and scattered in the ground-substance; (iv.) shorter sub- 

 tyJostyli {or styli) of scarcely one-half the length of the 

 preceding, almost entirely restricted to the dermal layer 

 A larger or smaller proportion of the megascleres (/.), 

 (///.) and {w.), are provided with a minute basal spina- 

 tion: this spination is the normal condition of dermal 

 styh and is of least frequent occurrence amono-st the 

 principal styli. Microscleres :-~ii.) Palmate isochdce of a 

 single kind varying in maximum length in the different 

 forms of the sponge from 20 to 25 n; {ii.) angiilately 

 curved toxa 60 to 80 y in length, and 2 to 2.5 u in 

 diameter. 



Introductory Remarks.~As the result of an examination of 

 -the figured specimen of Thalassodendron rubens var. lamella 

 and of undoubted specimens of T. rubens var. dura { = Clathria 

 rubens), I find that Lendenfeld has confused the descriptions 

 of these two sponges. The descriptions of their external 

 characters are proper, but those of their skeletal characters 

 should be mterchanged. To further add to the confusion, 

 \\ hitelegge, overlooking the essential points of difference 

 between the two, united them, together with T. brevispina as 

 a smgle species, Clathria rubens; of the five specimens whose 

 spicular characters he has separately described— though not 

 quite accurately— the second (labelled "Thalassodendron 

 rubens var. dura, No. 343"), as well as the third and fifth 

 belong to the present species {vide Whitelegge, Loc cit 

 pp. 86, 87). 



Description. — 



(a) Typical variety. 



The sponge is frequently— except for the presence of mar- ' 

 ginal digitations— perfectly lamelliform. More usually, how- 

 ever, growth proceeds by the rapidly-repeated multiplication— 

 always chiefly or entirely in one plane — of ascendant, cvlindri- 

 cal or slightly compressed, anastomosing branches, and' results 

 in the formation of a reticulated or fenestrated flabelliform 

 expansion. From this, a more or less continuous lamella may 

 in some cases be secondarily produced, through the gradual 

 obliteration of the interspaces by vertical ingrowth. It is 

 either owing to this latter mode of origin or because an actual 

 separation into branches is not quite fully accomplished, that 

 the surface in lamelliform examples is often, as Lendenfeld 

 states, "slightly grooved." In some instances the sponge 

 shows a marked disposition towards a freely branching habit, 

 but in no observed case is there, as is usual in the variety 

 multiporus, an entire absence of anastomosis or of confluence 

 of branches. The specimen of T. rubens var. lamella, figured 



