AND THALASSICOLLA. 75 



of the circumference, which is noticed in free Noctilucfe, and 

 the radiating filamentary branching striae beset with extremely 

 minute granules in the interior, were also characteristic of 

 the encysted bodies, which I should be the more indisposed to 

 separate from the NoctiluccE, from their possessing the most 

 remarkable luminous power. At present we want the key to 

 these remarkable phenomena, as well as all knowledge of the 

 development and course of life of the Noctilucce. 



After discussing the probable relations of Thalassicolla with 

 the Sponges and Polycystina — but without coming to any 

 positive conclusion on the subject, except, that in any case the 

 two forms of Thalassicolla and Collospha^ra must go together — 

 Prof. Miiller proceeds to describe a new genus, apparently 

 closely allied to them, under the name of Acantliometra, Miiller. 

 It consists of solitary, pelagic, silicious organisms, with a 

 gelatinous envelope to the body. They are motionless micro- 

 scopic creatures, constructed of a radiating silicious frame- 

 work, the long, usually polyhedral crystals of which are 

 disposed symmetrically in all directions, and meet in the 

 centre without forming any central cavity. The needles are 

 disposed in several decussating planes, and meet in the centre 

 with their conical truncated extremities. This construction 

 of the centre out of the conical ends of rays is observed in an 

 otherwise widely different structure insoluble in acid, which 

 Professor Miiller has described and figured, from the intes- 

 tinal contents of the Comatula mediterranean and which has 

 been termed by Ehrenberg Asterolampra pelagica. 



The Acanihometra differ fiom the ThalassicollcB in the 

 junction of their spicules in the middle, and in the circum- 

 stance that they are solitary, and, so far, are a distinct 

 formation. Like the PolycystincE they do not constitute 

 masses, but are distinguished from them by the absence of a 

 fenestrated shell, as well as by the construction of their 

 silicious skeleton. Actiniscus and Bacteriastrium differ from 

 Acanthometra in the circumstance that their rays lie in a 

 single plane and are united to a common centre. 



Of the PolycystincB, Professor Miiller remarks, that species 

 of Haliomma, Dictyospyris, Encyrtidium, Podocyrtis are occa- 

 sionally brought to the surface of the sea by currents and 

 other movements of the water ; at any rate it is certain, that, 

 though very rarely, they may occasionally be taken in tlie 

 drawing of a fine net, on larvae of Echinoderms, fully-formed 

 young Echinoderms, Medusa, Crustacea, Pteropoda, larvae of 

 Gasteropods, Conchifera, Annelids, &c., and on Infusoria ; 

 and the living Polycystina^ taken by him have been thus 

 picked up on pelagic objects. In the same way also an 



