112 THE VOYAGE OF H.M.S. CHALLENGER. 



margin run out 16 to 32 broad tentacular coronal pouches, and the same number of 

 alternating rudimentary ocular canals ; 8 separate adradial genitalia, grouped in pairs, 

 not distributed at equal distances. 



The genus Atolla, like the preceding Nauphanta, is one of the most remarkable 

 and morphologically interesting deep-sea Medusa brought to light by the Challenger 

 expedition. Both are very ancient remains of an extinct ancestral group of Discomedusae, 

 which clearly indicate the close connection of this order with the Cubomedusae and 

 Peromedusas. Atolla has a near relation in Collapsis, which is also an Antarctic deep- 

 sea Medusa, and which I have described in my System der Medusen (1879, p. 489, taf. 

 xxviii.). These two compose a special small group of deep-sea Cannostomae, which 

 I include provisionally as a sub-family of the Ephyridaa, but which it would be as well 

 to separate in future as an independent family of the Collaspidae. These two genera must 

 be essentially looked upon as Ephyridae, which are distinguished by their colossal size 

 and peculiar complications in the formation of the umbrella corona, and the coronal 

 intestine. The central umbrella disc, which is separated by a deep coronal furrow from 

 the surrounding umbrella corona, has, on the whole, the same formation as in the 

 Nausithoidae, especially Nauphanta. The wide, but short, quadrangular oesophagus, 

 cruciform in transverse section, is surrounded by eight genitalia, which in Atolla (as in 

 Nausicaa) are grouped in pairs, whdst in Colkqms (as in Nausithoe or Nauphanta) 

 they are adradially distributed at equal distances. The formation of the peripheric 

 umbrella corona differs entirely, as it is distinguished both by the increased number of 

 the marginal organs, and by special modifications of the structure. Whilst in all other 

 Ephyridae, Nausithoidae, as well as Palephyridae, the number of the sense clubs, tentacles, 

 and pairs of lobes invariably amounts to eight, in the Collaspidae it rises from sixteen to 

 thirty-two, and seems to vary in the same way as it does in most polynemal 

 NarcomedusEe. These remarkable Discomedusae are altogether so like the polynemal 

 Narcomedusae that at first I took them for gigantic forms of the latter. Another 

 peculiarity of the Collaspidae consists in the extraordinary development of their coronal 

 muscle. This is divided into two different, sharply defined wings, an inner or abaxial, 

 which is debcate and thin like a velum, and an outer or abaxial, which is dispropor- 

 tionately thick and divided into from sixteen to thirty-two areae. Immediately below it, 

 at the basis of each short tentacle, there are two thick spindle-shaped radical muscles, bke 

 those in the Peromedusae. The Collaspidae also resemble the Peromedusae strikingly in 

 the sculpture of the exumbrella, as its coronal part is divided b) r deep furrows into thick 

 polyhedral gelatinous pieces or pedalia. One half of these pedalia sustain the sense 

 clubs, the other half support the tentacles. The sense clubs and the pouches belonging 

 to them are small and scantily developed in Collapsis, and quite rudimentary in Atolla. 

 This retrograde formation of the higher organs of sense is probably a consequence of 

 adaptation to life in great depths of the sea. The formation of the coronal intestine is 



