34 Dr. C. Collingwood on some points in the Economy 



bay in the island of Cumbrae, Fu'th of Clyde. I received it 

 alive, and had it under observation, in a tolerably active state, 

 for two days. Supposing the animal to be a normal form, I 

 could not refer it to any British genus : nor did a comparison 

 with the characters of all the known genera of Nudibranchiate 

 Mollusca appear to throw much light upon the subject ; it 

 seemed to agree with no known species. I contented myself, 

 however, for the present, with preparing a full desciiption and 

 careful drawings of it while it was yet living, and taking every 

 opportunity of watching its movements. It was tolerably lively 

 — changing its place but little, however, though its body was in 

 constant nnotion, rendering it a difficult task to delineate it with 

 accuracy. The dorsal tentacles were singularly large, and were 

 covered with active cilia; the papillae, or what appeared to 

 answer to them, and which in the Eolididte are usually very 

 active, were in this specimen motionless ; and before death they 

 became detached and fell off, giving the little creature the ap- 

 pearance of being in shreds. It floated freely, foot uppermost, 

 on the surface of the water, as is the habit of Nudibranchs, and 

 did not produce any spawn. 



After death, I pursued the examination with the microscope, 

 and now discovered that the skin was loaded with spicula — a 

 fact which proved that it did not belong to the Eolididse at all, 

 that family possessing no spicula, and also that it was a member 

 of the family Dorididse, all of which, however, have more or less 

 conspicuous branchial plumes. These spicula were symmetri- 

 cally arranged, and very dense along the margin of the cloak ; 

 in shape they were generally cruciform, although a few were tri- 

 radiate, and some simple. The tongue was broad, and formed 

 of numerous small denticulated spines (eight or nine in a row), 

 with two longer spines at either side (PI. IV.). 



The fact of the presence of spicula, which could only be de- 

 termined after death, was an unexpected one, but came too late 

 to be of service in a further comparison of the animal with the 

 members of the family Dorididse, to which it evidently belonged; 

 and the absence of branchial plumes became now only more re- 

 markable, without assisting in the identification. I therefore 

 forwarded the drawings and description to my friend Mr. Alder, 

 knowing that his close acquaintance with the family, and great 

 experience in the critical examination of them, would be most 

 likely to elucidate the affinities of this little animal. Nor was I 

 disappointed : his answer, written with his usual kindness and 

 promptitude, was, " Upon carefully examining your drawings, I 

 cannot resist the conclusion that the animal is a young and un- 

 developed specimen of Triopa claviger." Upon turning to the 

 figure of this species in the Hay Society^s beautiful Monograph, 



