424 BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



None of the species which Schmidt lists is designated as the type 

 and neither of the new species is described in sufficient detail to be 

 recognizable. Lundbeck, 1902 (p. 99), in fact is in doubt whether 

 they even belong in the genus (still called at the time of his writing 

 Desmacella). Dendy, with justice, however, picks the first of the 

 new species, D. pumilio, as the type, but there is nothing in the diag- 

 nosis of D. pumilio to distinguish it from Biemna. The second 

 species, D. vagabunda, however, shows that Schmidt was using Des- 

 macella to cover sponges with tylostyles arranged in loose tracts as 

 well as those with tylostyles combined in definite fibers, like Desma- 

 cidon peachii Bowerbank, for which Biemna Gray had already been 

 arranged although it had been lost sight of. D. vagabunda might 

 then possibly, in spite of its inadequate description, have been se- 

 lected by a subsequent author as the type of a genus, Desmacella 

 sens, str., marked off from Biemna by the halichondrioid character 

 of its skeletal framework. This step, which was permissible (Inter- 

 national Kules of Zoological Nomenclature, article 30, g, Proc. Ninth 

 Congress, 1914), but which neither was nor is obligatory, was not 

 taken. Instead the genus, sharply enough conceived by Topsent, 

 1892, but given a name (Biemma) which had to be withdrawn, was 

 designated by Thiele Tylodesma. To bring in again the unfortunate 

 term Desmacella, as Dendy proposes, and employ it at this late date 

 for the genus in question would surely be an unwarranted step. 



Tylodesma as a generic name should then stand, if the genus it- 

 self stands as a group distinct from Biemna. Dendy, 1921&, is 

 evidently doubtful whether both genera should be retained. If 

 Tylodesma (or, as he would call it, Desmacella) is retained, he 

 thinks it can only be on the ground that it lacks the rhaphides (or 

 trichodragmas) , which he would make a differential feature of 

 Biemna. But to exclude species from Biemna because they have 

 no rhaphides would bring more trouble, in that we would run coun- 

 ter to established practice: See Topsent's definition of Desmacella 

 (=Biemna), 1892 (p. 83) ; Topsent, 1904 (p. 225) ; Hentschel, 1912 

 (p. 353, Biemna truncata with no rhaphides), (p. 354, Tylodesma 

 microstrongyla- with rhaphides). Hallmann, 1916, 1917, also has 

 interesting propositions for the subdivision of this group of species 

 into genera. However, it seems to me that all the species would bet- 

 ter be combined in one genus, Biemna, within which subgeneric 

 types (see under Tetilla for instance) could doubtless be set up. 

 We would thus have a genus of reasonable scope and identical with 

 what Schmidt understood by Desmacella after he had excluded 

 Hamacantha (1880). For a different set of propositions concern- 

 ing the grouping of these species, see Hallmann 1916. Dendy, 19215, 

 it may be added, now places them in the Desmacidonidae. 



