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THE SPONGES. 



185 



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1870. 

 1880. 

 1885. 

 1887. 

 1887- 

 1892. 



1894. 

 1902. 

 1903. 



POECILOSCLERIDAE Topsent (1894). 



Tylodesma Thiele. 



Desmacella pars 0. Schmidt, 1870, p. 53. 



Desmacodes O. Sclim. pars Vosmaer, ] 880, p. 104. 



Gellius Gray pars Vosmaer, 1885, p. 28. 



Gellius Gray pars Vosmaer, 1887, p. 349. 



Desmacella Schmidt, Ridley & Dendy, 1887, p. 58. 



Biemma Gray -f- Desmacella 0. Scliiii. pars Topsent, 1892, p. 80. 



Biemma Gray, Topsent, 1894 a, p. 11. 



Biemma Gray, Lundbeck, 1902, p. 82. 



Tylodesma Thiele, 1903, p. 944. 



Thiele (1903., pp. 943-44) remarks that Schmidt, when he established the 

 genus Desmacella (1870, p. 53), included in this genus, along with his 

 several new species, D. (Ilymedesmia) johnsoni (Bwk.), which was the type 

 of Hamacaniha Gray (1867, p. 538) ; that Desmacella is therefore a synonym 

 of Hamacantha, and must be cancelled, as Vosmaer has already pointed out. 



Thiele further calls to mind that Gray, in establishing the genus Bicmna 

 (1867, p. 538), names as the only certain species Biemna {Desmacidon 

 peachii Bwk.) ; that this species is commonly assigned at the present time 

 to Desmacella; and that the name Desmacella as used in the customary 

 sense of to-day should be replaced by Biemna. 



For the group of species included in the genus Biemna [sensu Topsent, 



1892, 1894 a), Thiele proposes the name of Tylodesma. 



Thiele's contention that Desmacidon peachii Bwk., which has been 

 commonly assigned since 1870 (O. Schm. 1870, p. 77) to Desmacella, and 

 similar sponges should again be designated as species of Biemna Gray, and 

 that Biemma sensu Topsent (1892, p. 80) cannot be maintained, is, I think, 

 incontestable. (Rules for Zool. Nomenclature in Verhdlg. v. Intern. Zool.- 



Congress, p. 966, Art. 2.) 



The name Desmacella is strictly a synonym, and Vosmaer (1885, p. 28; 

 1887, p. 221) and Thiele (1903) are therefore justified in cancelling it. The 

 new species described by Schmidt under this name (1870, p. 53) neverthe- 

 less constituted a new group, which was homogeneous and is identical with 

 Biemna as defined by Topsent in 1892, and recently again defined by 

 Lundbeck (1902). Ridley and Dendy (1887, p. 58) regard these species as 

 " the types of the genus Desmacella" and retain the name. Vosmaer 

 (1880) designates them Desmacodes, but this name cannot be retained for 



