ECHINOIDEA. I. 153 



Echinus rarispiitits V,. (). Sars. 

 — microstoiiiii \V>\'. Tlioiiis. 

 Principal literature: Diiben & Koreii: Ofvers. af Skaiidinaviens Echinodermer. p. 266, 268. — 

 M. Sars: Norges Echinodermer. p. 92. Middelhavets Littoral-Fauna, p.m. — G. O. Sar.s: Nye Echino- 

 dermer fra den norske Ky.st (Vidensk. Selsk. Forhandl. Kri.stiauia. 1871. p. 23). Bidrag til Kund.skaben 

 om Dvrelivet paa vore Havbanker. Ibid. 1872. p. 104. — Aga.ssiz: Revi.siou of Echini, p. 296, 489. 

 6. p. 77. tBlake Echini 19). p. 39. — W y v. Thoni.sou: Porcupine Echinoidea (395). p. 744. — 

 Danielssen: Echinida. Norske Nordh. Exped. (no), p. 3. — E. v. Marenzeller: 269. p. 13. 270. p. 20. 

 — Koehler: 217. p. 121. Notes echinologiques (221). p. 20. 229. p. 23. — Prouho: 327. p. 8. — Hoyle: 

 Revised List of Brit. Echinoidea (202). p. 413, 415. — Bell: Catalogue of Brit. Echinoderm.s. p. 146— 49. 

 With regard to the other literature tlie reader is referred to Revi.son of Echini , Bell's Catalogue'^, 

 and Ludwig's -Die Echinoderuien des Mittelmeeres (256). 



This species, I think, is the one that has caused most difficulties to the sy.stematists. As 

 shown bv the s\nouvms enumerated above, a whole series of species has been established on more or 

 less distinct forms of it; some of these, however, are now connnonly regarded as .synonyms, while 

 others [norvegicus, microsto>na^ and parth' Flemingii) are constantl>- mentioned as independent species, 

 although expressions as critical species (Wyv. Thomson. Op. cit), it seems almost hopeless to 

 attempt to distinguish the species of Echinus known as E. rlrgaiis^], E. norvegicus^ E. iiiclo, and E. 

 Flemingii (Agassiz 9. p. 39) sufficiently show the difficult)- of distinguishing between them. The 

 best founded of these species is, no doubt, nomcgicus^ and so long as I had only examined the material 

 from the «Ingolf»-Expedition, and what was otherwise found in our museum of this form, I also 

 felt persuaded that it was a distinct species. After having collected a considerable material at the 

 Faroe Islands during the summer of 1S99, and especially after ha\-ing received a considerable number of 

 specimens of all .sizes from the Mediterranean from Prof. E. v. Marenzeller, I have got to the result, 

 however, tliat the whole can onl\- be interpreted as one very \-ar>-ing species, among the numerous 

 forms of which three tolerably distinct varieties may, however, be distinguished: var. incdifrrraura, 

 Flemingii, and norvcgicus. 



The northern specimens are generally easily referred to respectively norvegiats or Flemingii : 

 especially it seems that at the Norwegian coasts specimens are rather seldom found, which are only 

 with difficulty decidedly to be referred to one or the other of the mentioned forms. Most of the men- 

 tioned specimens from the Faroe Islands, on the other hand, it was impossible with certaint\- to refer 

 to one or the other variet>-. In the Mediterranean a third, ver\- large form occurs, which I have called 

 var. ineditcrranca\ it does not seem to be found in the northern Atlantic, but in return var. Flemingii 

 is apparenth- not found in the Mediterranean. On the other hand var. iiorvegicus occurs in both seas. 

 But in the Mediterranean this latter scarcely occurs as a marked variety; in the material received 

 from Prof. v. Marenzeller, at all events, all possible transitions were found between the genuine iior- 

 vegicus and var. inediterranea. In the first of the essays quoted above v. Marenzeller has referred 

 the specimens before him to E. norvcgicus after a comparison with northern specimens of this form; 

 in the latter he has, on the basis of a greater material, referred the whole to Ech. acutus. I must 

 M That E. elegans is mentioned in this connection is owing to a wrong interpretation of this species (comp. pp. 99, I45)- 



The Ingolf-Expedition. TV. I. 20 



