183 



work more precise by his introduction of a more definite spicular basis of 

 classification. The following gives precisely his important addition : " I know 

 only the spicules of the caMienchynia of /. //ippi(r/s, which exhibit spindles beset 

 with spiny warts, of which the simplest are in sixes, eights or twelves. Some 

 are simple clubs, and probal)ly represent those of the cortical layer. The warts 

 on one side are smaller than those on the other. Tetra-radiate forms are not 

 uncommon. The size of the largest spicule is 01>^ mm." The only other 

 species referred by him to this genus are /. moniliformis, Steenstrup, /. r/rarifi.s- 

 [Mopsea gracilis), Lamouroux. 



Studer in 1878 established a new species, /. antarrtica, and G. von Koch, 

 in 1887, referred to this genus another form under the name /. ncrrpolitana. 

 Of this and of the closely allied Jsix elomjata (Esper), von Koch gave a detailed 

 description, eventually deciding, however, that both should be referred not to 

 his but to Isidella. 



Wright and Studer, in the " 'Challenger' Keport," vol. xxxi., 1889, tersely 

 sum up the characters of his, and accept Kolliker's description of the 

 spicules of /. hippuris as typical of the genus, placing it in the Family Isidae, 

 Suli-family Isidina*. At the same time the genera Primnoisis and CaUisis were 

 added to the classification, and this necessitated the abolition of certain species 

 formerly placed in the genus his. 



Thus we see that since the genus was established by Linni^us in 1737 no 

 fewer than nineteen species have been added by various authors, but, strange 

 to .say, only one now remains as an authentic species, riz., I. hippuris, 

 Linuccus. The following table represents these s})ecies, the second column 

 indicating their place under the present system of classification and nomen- 

 clature : — 



Isis antarctica, Studer, 1878. 



I. aurantia, Esper, 1797. 



I. capensis, Studer, 1878. 



J. coccinea, Esper and Studer, 1786 ; Gmel. ; 



Esper. 

 I. coralloides, Lamarck, 1836 ; Milne-Edwards 



and Haime, 1857. 

 I. dichotoma, Linnaeus, 1737; Lamarck, 1836. 

 I. dichotoma, Pallas, 1760. 



Mopsella dichotoma, Gray, 1857. 

 I. eloiigata, Esper, 1797 ; Milne-Edwards and 



Haime, 1857 ; Lamarck, 1836. 

 I. encrinula, Lamarck, 1836. 

 I. erythracea, Lamarck, 1836. 

 I. flexibilis, Pourt., 1868. 

 I. gracilis, Lamarck, 1836 ; Lamouroux. 

 I. gregorii. Gray, 1868. 



Primnoisis Antarctica, Wright and Studer, 1889. 

 Melitaa aurantia, Gray, 1857. 

 Primnoisis capensis, Wright and Studer, 1889. 

 Melitaa coccinea, Gray, 1857, 



Isidella (?) coralloides. Gray, 1857. 



Mopsca dichotoma, Wright aud Studer, 1889. 

 Melitodes dichotoma, Wright and Studer, 1889. 



Isidella elongata, Gray, 1857. 



Mopsea encrinula, Gray, 1857. 



Isidella elongata. Gray, 1857. 



Callisis flexibilis, Wright and Studer, 1889. 



Isidella elongata, Gray, 1857. 



