12 



HJALMAR BROCH. 



[REP. OF THE "MICHAEL SARS" NORTH 



vious work Haeckel 1 ) introduced a closely related genus 

 Collaspis, which, with the single species C. Achillis, has 

 later been referred to Atolla. Only a few years later 

 Fewkes 2 ) described two new species of the genus from 

 the Gulf-Stream, viz. A. Bairdi and A. Verrilli. The for- 

 mer species was taken by the Plankton Expedition) 3 , and 

 some years later Maas 1 ) described two new species A. 

 gigantea and .4. Alexandri. Up to 1897 twenty-six speci- 

 mens of Atolla were known, distributed among the species 

 as follows: 5 A. Wyvillei, 1 A. Achillis, 5 A. Bairdi, 12 A. 

 Verrilli, 1 .4. gigantea and 2 A. Alexandri. They were 

 all taken in dredges, and came into the hands of the 

 investigators in a more or less badly damaged state. 



Excellent material was obtained during the "Valdivia" 

 Expedition and Vanhoffen had an opportunity of investi- 

 gating in a living condition most of the 54 specimens 

 taken. His report 5 ) gives details regarding the genus Atolla, 

 including three of the previously known species, besides 

 two new ones, viz. A. Valdiviae and A. Chuni. — In the 

 same year Agassiz and Mayer 6 ) again mention A. Alex- 

 andri. In two subsequent papers Maas gives further details 

 of nine specimens of A. Valdiviae -1 ) and A. Bairdi 8 ). Browne 

 mentions A. Bairdi from the Biscayan 9 ), A. Chuni and 

 A. Wyvillei 10 ) and again A. Wyvillei n ) from the antarctic 

 seas. The last mentioned species is not restricted to the 

 antarctic area, for Bigelow 12 ) has recently examined no 

 less than nineteen specimens from localities near the Gala- 

 pagos-Islands and South California in the Pacific Ocean. 



Lastly we must mention a species lately described 

 by Hartlaub 13 ) under the name of A. tenella, from the 

 arctic area. The distinguishing character: "des paires 

 de taches pigmentaires exombreliaires" is also found in 

 A. Bairdi and Hartlaub's description proves the identity 

 of these two species. 



If we consider all the specimens of Atolla hitherto 

 investigated we find that the number does not exceed 

 100, which must be assumed to belong to seven species. 



Two of them, viz. A. Bairdi and A. Verrilli, have been 

 reported from Atlantic and arctic localities, and A. Wyvillei 

 may also be expected from the Atlantic in accordance 

 with its occurrence in the Pacific Ocean. 



Atolla Wyvillei Haeckel. 



Curiously enough a large typical specimen of A. 

 Wyvillei was found among the very many specimens of 

 Atolla brought home by the "Michael Sars". It was taken 

 at Stat. 62 in Lat. 36° 52' N, Long. 39° 55' W, in 1500 

 metres. The broad and conspicuous radial furrows of the 

 central disc and the strongly marked longitudinal furrow 

 of the pedalion distinguish this species from the other 

 Atlantic species. The single specimen is darkly pigmented, 

 the pigment of the exumbrella extending a little way up 

 into the radial furrows of the central disc. 



The range of the species is considerably extended by 

 this new locality. As already mentioned Bigelow (1. c.) 

 has pointed out that A. Wyvillei occurs near the Gala- 

 pagos-Islands and off the southern coast of California in 

 the Pacific, though it had previously been considered an 

 antarctic species, and we may therefore expect to learn 

 of its occurrence in the South Atlantic also. It is rather 

 surprising to find that its northern limit must now be 

 drawn at lat. 37° N. 



Atolla Bairdi Fewkes. 



If we except the single specimen of Atolla Wyvillei, 

 all the other specimens of Atolla— more than 200— brought 

 home by the "Michael Sars" from the Atlantic Ocean 

 belong to one species. It must be granted that many of 

 them might be referred to A. Verrilli, but the separation 

 of A. Verrilli and A. Bairdi seems, in fact, to be due to 

 the circumstance that nobody has hitherto had sufficient 

 material for a critical examination of the doubtful indi- 

 viduals. 



') System der Medusen, Jena 1880, p. 489. 



2 ) Report on the Medusae coll. by U. S. Fish Coram. Steamer "Albatros", in the region of the Gulf-Stream. (U. S. Comra. of fish 

 and fisheries. Rep. of the Commissioner for 1884) p. 934. 



3 ) Vanhoffex: Die Akalephen der Plankton-Expedition (Ergebn. der Plankton-Expedition. Bd. II), Kit 1 1892, p. 16. 



4 ) Die Medusen (Rep. Explor. West Coasts of Mexico, Central and South America, Galapagos Islands, by the U. S. Fish Comm. 

 Steamer "Albatros"— Mem. Mus. Comp. Zool. Vol. XXIII), Cambridge U. S. A. 1897, p. 80. 



s ) Deutsche Tiefsee-Expedition, Bd. Ill, p. 5. 



«) The Medusae (Rep. Scientific Res. Exped. Tropic. Pacific— Mem. Mus. Comp. Zool., Vol. XXVI) Cambridge U. S. A. 1902. 

 7 ) Die Scyphomedusen der Siboga-Expedition (Siboga Expeditie, Monogr. XI) Leiden 1903, p, 17. 



e ) M6duses provenant des Campagnes des yachts Hirondelles et Princesse Alice (Res. Camp. Scient. Prince de 

 Monaco. Fasc. XXVIII), Monaco 1904, p. 49. 



°) The Medusae (Biscayan Plankton, Trans. Linn. Soc. London Zoology, Vol. X) 1906, p. 179. 

 10 ) The Medusae of the Scottisch National Expedition, (Trans. Roy. Soc), Edinburg 1908, p. 240. 

 u ) Medusae (National Antarctic Expedition, Natural History, Vol. V) London 1910, p. 47. 



12 ) The Medusae (Rep. scient. res. eastern tropical Pacific "Albatros"— Mem. Mus. Comp. Zool., Vol. XXXIII), Cambridge 

 U. S. A. 1909, p. 38. 



13 ) Meduses (Due D'Orleans: Croisiere oceanographic dans la mer du Grenland 1905) Bruxelles 1909, p. 17. 



