j, 2 PORIFERA. II. 



to a very slight amount. Spicula: Megasclera: fin: skeletal spicules styli\ most frequently spiiied, sometimes 

 smooth, the dermal spicules diactinal, strongyla, tornota, tylota, or similar forms, the ends may be vari- 

 ously formed, and spined or smooth ; microsclera, ancorce. spatuliferce, sometimes of two forms, most fre- 

 quently three-toothed, sometimes with more teeth; further sigmata may be added. 



In 1862 O. Schmidt established the genus Myxilla with the species rosacea Lieberkiihn. In 

 1867 Gray established the genus Dendoryx, and as the first species under it he mentioned incrustans 

 Johnst. In 1887 Vosmaer, in Porifera, Bronn's Klassen und Ordnungen , has the families Dcsma- 

 cidonida- and Ectyouidcc, and he places Myxilla to the former family, and has Dendoryx with a query 

 as a synonym to Hastatus, which, as is well known, is identical with Myxilla. In the same year Ridley 

 and Dendy in Challeng. Report, under the family Dcsmacidonidce, have the subfamilies Esperelliiur 

 and Ectyoniucr, and here they place the genus Myxilla to the latter subfamily. They render a detailed 

 account of the fact that the genus comprises as well species with accessory spicules as species with- 

 out such spicules, but they have not wished to divide the genus. In 1S8S Top sent (Arch. de. Zool. 

 exp. et gen. Ser. 2, V, bis, 114) revives Gray's Dendoryx, and in 1892 he places the species without 

 accessory spicules in Dendoryx, while he places the species with such spicules in Myxilla. Then 

 Dendoryx is placed under Esperellincr and Myxilla under Ectyonince. Thiele, however, in 1903 

 (Kieselschwamme von Ternate, II, Abhandl. der Senckenberg. nat. Gesell. XXV, 953) renders an account 

 of the fact that the genus Dendoryx, as Topsent understands it, ought to be called Myxilla, as the 

 typical species of Myxilla, rosacea Lieberk., according to Topsent (Mem. de la Soc. zool. de Fr. VII, 15, 

 footnote 4) is identical with incrustans Johnst. Even if this view, as will be seen below, is not correct, 

 the name of Myxilla will have to be used, as rosacea is, at all events, a species without accessory spicules. 



1. M. incrustans Johnst. 

 PI. IV, Figs. 6, 7. PI. XIV, Fig. 3 a-h. 



1842. Halichondria incrustans Johnston, A History of Brit. Spong. and Lithophytes, 122, PI. XII, fig. 3, 



PL XIII, fig. 5. 



1842. Halichondria saburrata Johnston, ibid. 120, PI. XI, fig. 3. 



1866. Halichondria incrustans Bowerbank, Mon. Brit. Spong. II, 249, 14. 



1870. Isodictya fmbriata O.Schmidt (non Bow.), Grundziige einer Spongienf. des atlant. Gebiet. 56. 



1874. Halichondria incrustans Bowerbank, 1. c. Ill, 108, PI. XLIV, figs. 7 — 12. 



1885. Myxilla barentsi Vosmaer, Bijdr. tot de Dierk. i2te Aflev., 3die Gedelt, 27, PI. IV, figs. 15—16, 



PI. V, figs. 56-59. 

 1885? Hastatus Robertson/ Fristedt, Kgl. Sv. Vet. Akad. Handl. 21, Nr. 6, 34, Tab. Ill, Fig. 4 a— b. 



1886. Desmacidou incrustans Marenzeller, Die osterreich. Polarstat. Jan Mayeu, III, 10, Tab. I, Fig. 2. 

 1887? Hastatus Robertsoni Fristedt, Vega-Exp. Vetensk. Iakkt. IV, 442. 



1S88. Dendoryx incrustans van typica Topsent, Arch, de zool. exp. et gen. Ser. 2, V, bis suppl. 118, 



PI. VI, fig. 16 a. 

 1890. Dendoryx incrustans Topsent, Mem. de la Soc. zool. de Fr., 201. 



