Marine Aquarium. 



6233 



In a cockle there is ons on the umbone earned through but not com- 

 pleted, and another, completed, towards the middle of the valve ; in 

 a Donax it is of irregular shape, and on the hinge-line between 

 the valves. The Natica maintains communication with the surface, 

 when buried in the sand, by a good-sized hole, that probably com- 

 municates with the branchial chamber on the left side. When 

 creeping above the sand, the left posterior angle of the mentum 

 is raised so as to admit the water to the gills. The tentacles are but 

 little developed, and laid back against the shell when the animal is 

 first exserted, but when it becomes more famiharised with its situa- 

 tion they stand erect, of considerable length, arcuate, with their con- 

 vexity forwards. The drawing in the ' British Mollusca,' by Mr. 

 Spence Bate, is mostly incorrect ; Arthur Adams has drawn it better, 

 but, as in other figures of his, the animal seems somewhat contorted. 

 The mouth is provided with two horny jaws, of the same character as 

 that of Triton, figured in the ' Manual of the Mollusca \ they are 

 irregularly triangular, striate, with one side strongly serrated. The 

 lingual ribbon is less than a third of an inch in length. The jaws 

 are horny brow'n, the buccal mass red, the proboscis white ; the 

 latter, when exserted, seems rather thick, but must be capable of 

 attenuation to pass through the small holes it makes. Though it 

 devours its victims pretty completely, there is always some animal 

 matter left, which blackens all the sand round it when it decays. 

 Unless the shells are removed as soon as the Natica leaves them, the 

 sand in which it is kept becomes after a while unfit for use. The 

 former expedient is difficult to adopt, as the only indications of an 

 animal's death are the disappearance of its siphons, and the presence 

 of the Natica in its neighbourhood. Natica can creep up the glass, 

 but does not adhere firmly ; it leaves a slimy trail. 



Turbonilla, Loven. These minute animals afford strong proof of 

 the utility of the aquarium to the working student. Speaking of the 

 difficulties of, and perseverance required in, the observation of these 

 little creatures, Mr. Clark says they must be studied " with a regular 

 supply of fresh specimens, as torpidity always ensues in less than 

 twenty-four hours." As far as my own limited experience extends, 

 they will remain lively in the aquarium for at least a month or so. 

 I can confirm his statement that T. (Chemnitzia) pusilla has the foot 

 produced behind and pointed, while T. (Chemnitzia) elegantissima is 

 said to have it rounded behind and shorter. It creeps quickly over 

 the sand and glass, but very frequently falls off" the latter. The shell 

 is dragged rather than borne ; the mentum is carried in the same 

 XVI. 3 c 



