Marine Aquarium. 



6237 



marked. They are more active than the mature ones. Like all 

 byssiferous bivalves, they can detach their byssus and move about. 

 When the water is insufficiently aerated they usually move to the 

 surface. Their track is marked by the detached threads they spin to 

 assist them in climbing. 



Modiola Modiolus I have found hardier than the mussel and more 

 sedentary. They seldom, if ever, move from where they are placed. 

 The mantle is of a dirty brown with white spots, and its margins are 

 plain ; the anal siphon is distinct from the branchial, and has some- 

 times a laterally-compressed conical appearance. 



Crenella marmorata can be easily kept, and its siphonal develop- 

 ments are rather peculiar : the anal siphon is tubular, and can be 

 protruded nearly as long as the shell ; the branchial gape extends 

 from half-way up the anal siphon to the middle of the ventral range, 

 opening wide enough to show the branchiae ; the two margins of the 

 mantle that form it are plain and often much protruded. The foot 

 can be drawn out to twice or thrice the length of the shell. The 

 siphons are white tinged with purplish red. They are active and 

 lively animals, and often conceal themselves in crevices or tufts of 

 weed. They do not seem to suffer from being cut out of the tests of 

 Ascidiae : my specimens were obtained in this manner. 



The habits of the sand bivalves, Mactra, Tellina, &c., are all 

 similar, and they require to be kept in the same way, viz., in a 

 bottom of pure sand. They seldom move when once buried. I 

 have preserved several species without difficulty, but, as they show 

 nothing but the tips of their siphons, they are not very interesting. 

 The siphons of bivalves vary much in length, but they are often 

 figured and described as shorter than they usually are. Cockles da 

 not bury so readily as the others, and their short siphons oblige them 

 to keep near the surface. Tellina solidula has a peculiar habit of 

 writhing the inhalent siphon, and touching the surface of the sand 

 with its tip, sucking in small particles, which can be seen through the 

 translucent tube. T. tenuis seems to be destitute of this peculiarity. 

 Young tapes will suspend themselves to the glass sides like young 

 mussels. 



Saxicava lives well, but is liable to be stifled by the thick, matted 

 and slimy Confervae often common in long- established aquaria. 

 They either live uncovered, or bury themselves in the shingle. The 

 siphons of S. rugosa are generally nearly as long as the shell. 

 When the Confervas gathers round them they are entirely retracted, 



