NUDIBRANCHIATA OF THE L.M.B.C. DISTRICT. 151 



{Pleuronectes platessa), a few small thornback rays (Rata 

 clavata), turbot {Rhomhus madumus), and one brill {Rhomhus 

 Icevis), and on one occasion had some young cod {Gadus 

 morrhua). The average size of these flat fish is six or 

 seven inches in length, and there are over sixty of them 

 altogether in the tank. 



C is an octagonal centre or table tank with a sandy 

 bottom, measuring 4 feet 6 inches in diameter and 17 

 inches in depth, and holding about 100 gallons of water. 

 It contains various small fishes, viz., bullhead (Cotfus 

 hufniUs), wrasse or goldsinny {Ctenohifnnis rtipestris), J)0gge 

 (Ac/onus cataphractus) , gemmeous dragonet {GalUonymas 

 hjra), five-bearded rockling {Moiella Diustela), viper w^eever 

 {Trachinus vipera), and young cod {Gadus morrhua). 



All these fishes were in a thoroughly healthy condition, 

 and some of them had been living undisturbed in their 

 tanks for periods varying up to four years. The water in 

 the tanks is kept aerated, and in constant circulation by 

 a water engine. The fish are usually fed upon mussels, 

 cockles, and occasionally worms, which are thrown in at 

 the top of the tank and allowed to sink slowly through the 

 water. Such food matters are usually seen at once and 

 eagerly pounced upon and eaten during their descent. We 

 adopted the same plan in putting most of the nudibranchs 

 into the tanks ; and as, in anticipation of the visit to the 

 Aquarium in the afternoon, the fishes were not fed on the 

 days we intended to experiment with them, they had been 

 fasting for about twenty-four hours, and so may be regarded 

 as being unusually eager to seize any object dropped into 

 the water. At the beginning, and again at the end of each 

 day's experiments, we threv/ a couple of cockles or mussels 

 into the tank, and found that they were at once caught 

 and bolted in the usual manner. 



