1914-] N. Annandale : Sponges of Lake Baikal. 145 



Type-species : Lubomirskia bacillifera, Dybowski. 



The embr^^os, which are often abundant in B. bacillifera, 

 resemble those of Lubomirskia, but the free-swimming larva is 

 unknown. 



The following species must be assigned to this genus : — 

 Lubomirskia bacillifera, L. papyracea and L. intermedia, Dybowski, 

 L. tscherskii, L. fusifera and (probably) L. baikalejisis var. e, Souk- 

 atschoff . and L. irregularis , Swartschevski. All these sponges are, 

 so far as is known, found onh^ in Lake Baikal. 



I have examined numerous specimens of B. bacillifera and 

 B. intermedia, both of which I assigned in 1913 (or rather in 191 1) 

 to the same genus as Lubomirskia baicalensis. This was, however, 

 before I had attempted to dissect out individual fibres from the 

 skeleton or to use pyrogallic acid as a stain in their examination. 

 When I attempted to isolate the fibres an essential difference at 

 once became apparent : it was impossible to disassociate them 

 without breaking them into fragments, and they had none of the 

 springiness and elasticity of those of Lubomirskia. They were 

 moreover, so fragile that attempts to brush them clean always 

 ended in disaster. Fragments of the skeleton, cleaned as far 

 as possible in running water, were then stained in pyrogallic 

 solution, and the difference in the structure of the skeleton- fibres 

 of the two genera at once became clear. There is in Baikalospon- 

 gia no horny fibre-sheath, but the fibres are built up in a ladder-like 

 formation of groups of spicules, which adhere together in bunches 

 and series of bunches by means of thin veil-like films of horny or 

 chitinoid substance secreted at the points at which they are actually 

 in contact. This formation is identical with that found in the 

 skeleton of the harder species of Spongillidae (c/. plate ix, figs. 3« 

 and 4) and also in many sponges of the subfamily Renierinae. 



In assigning B. bacillifera and its allies to this subfamily I 

 rely rather on negative than on positive evidence, placing them 

 there rather because they are neither Spongillidae (having no sub- 

 dermal cavities) nor ChaHninae (having no horny sheath to their 

 skeleton-fibres) than on account of au}^ definite character they 

 possess. There are two genera Nudospongilla (Spongillidae of the 

 subfamily Potamolepidinae) and Metschnikowia (probably Renieri- 

 nae) to which they bear a very close resemblance in many charac- 

 ters, but both of these genera occupy' an anomalous and somewhat 

 unsatisfactory position. 



Nudospongilla,^ a genus of my own, is confessedl}^ no more 

 than a convenient generic appellation for those freshwater sponges 

 in which the microscleres have disappeared but the skeleton has 

 not the hardness or compactness of Potamolepis, Marshall. The 

 skeleton-spicules may be either smooth or spiny and in the type- 

 species {N. coggini, pi ix, fig. 5) have a form not unlike those of 

 some varieties of B. bacillifera; they are invariably amphioxous 

 or practically so, whereas those of Potamolepis are amphistrongylous. 



i jfonni. As. Soc. Bengal 1913, p. 62. 



