ZOOLOGY AND BOTANY, MIGKOSCOPY, ETC. 



257 



the parenchyma the same jilan is ado^jted, omitting the potash. For 

 the isolation of spicules, the method recommended by Bowerbank in 

 his monograph of British sponges is followed, with the addition of one 

 or two washings of the dissolved mass of spicules in alcohol previous 

 to mounting ; if a skeleton is especially refractory owing to its large 

 proportion of horny matter, it is teased, and the loosened spicules are 

 then mounted. 



The systematic part of this work is devoted to the sponges of 

 Lake Baikal,* vs^hich are shown to be much more numerous and 

 interesting than any previous observer has ever found them to be ; 

 and to a re-description of the species of Veluspa, Reniera, and Metscli- 

 nikowia, described chiefly by Miklucho-Maclay and Grimm, from the 

 White, Black, and Caspian seas. The Spongillidce are reserved for a 

 future memoir. 



The Baikal sponges were obtained from depths of from 2 to 50 

 metres, or as dead beach specimens ; the greater depths of the lake, 

 extending to as much as 1370 metres, are still unexplored. 



All the forms (four in number, besides varieties) belong to a new 

 genus, Luhomirakia, based on the old species of Pallas, Spongia baica- 

 lensis, and characterized as follows : — Shape very various ; the skeleton 

 consists of a set of fibres perpendicular to the surface, united by short 

 horizontal ones. The fibres are almost wholly composed of siliceous' 

 spicula, which lie 6-14 thick in the perpendicular, and 1-6 thick in 

 the horizontal fibres ; the spicula are either fusiform or bacillar, with 

 rounded ends ; their ends are sometimes minutely spined. The flesh 

 spicules are irregularly scattered and smooth, but otherwise differ from 

 the skeleton forms only by their inferior dimensions. Pores scattered 

 over the entire surface ; oscula various in shape, but almost always of 

 complicated outline. Keproduction perhaps by ova ; no gemmules 

 occur as in Spongilla. This interesting genus differs from Spongilla 

 in the shape of the oscula, in that of the spicula, which are not of 

 the peculia'" fusiform type of Spongilla, and in the absence of gem- 

 mules. The type species, L. haicalensis, is stated to vary in shape 

 from branching to simple, horizontally-extended, cylindrical forms ; 

 the latter are younger stages of the former. The proportions 

 between the dimensions of the stem and branches in different speci- 

 mens are tolerably constant, as also are the characters of the pores 

 and oscula. The perpendicular fibres are 0*11 mm. thick. 



To show the nature and extent to which variability occurs in the 

 size of spicules in sponges of this kind, the measurements of tea 

 skeleton-spicules of the typical form of this species may be given. 



Cf. a preliminary account in Zool. Anzcigcr, i. (1878) pp. 30 and 53. 



