448 THE OPISTHOBRANOHIATE 



under the Hoe whenever they were visited at low water. They 

 were congregated generally in groups of five or six together, but 

 not infrequently I found isolated couples. They were most plentiful 

 on rocks covered with the red gregarious Tunicate, Styela grossularia, 

 and on this and elsewhere their spawn was abundant. Small indi- 

 viduals {i. e. of I inch and under) were not found upon the rocks at 

 all, nor were they to be obtained with the dredge in deeper water. 

 Veligers, however, were regularly taken during the early spring 

 months in the surface-net. During June the numbers of mature 

 individuals found on the shore, and at the same time the quantity of 

 spawn, became appreciably reduced, and July found them more or 

 less rare. Very small specimens were noticed in the contents of 

 the dredge in June, and were frequently taken during July and 

 August. My observations were here interrupted for several weeks, 

 but on October 8th a specimen rather over | inch in length was 

 trawled in the Cattewater ; next day one of the same size was dredged 

 on Zostera in Cawsand Bay, and on the 10th I found one also under 

 a stone at extreme low water (spring tide) in Rum Bay. The dredge 

 continued to bring up specimens between | and f inch long off 

 the Duke Rock and elsewhere, but they were never in such numbers 

 as were those of July. On November 22nd during a spring tide I 

 found a large one on a stone at Drake's Island, and on the 25th in a 

 small crevice of rock under West Hoe, rather high up between tide- 

 marks, I found two large ones together. I could find none at this 

 time under the bathing pond. I brought the two large ones to the 

 Laboratory, and placed them in an aquarium ; on the 6th of December 

 one of them deposited some spawn, and another piece was laid three 

 days later. On the 20th of February this year, full -sized mature 

 specimens, in considerable numbers, were copulating and depositing 

 eggs on the rocks below the Laboratory, below the bathing pond, 

 and at Drake's Island. At Drake's Island one individual was under 

 I inch in length. 



It is obvious from these facts that at Plymouth the habits of the 

 species and its rate of growth are very much as Alder and Hancock 

 found to be the case on the coast of Northumberland ; and this in- 

 duces me to believe that at St. Andrews also more detailed observa- 

 tions would lead to a similar conviction. 



The rate of growth of the species is to some extent indicated by 

 the following measurements of the individuals dredged at Plymouth 

 during the present year up to the end of August. 



June 26th. — One specimen dredged off the Duke Rock, just over 

 I inch in length, and having three branchial plumes only on each side. 



June 27th. — One specimen -f^ inch long, taken among weeds with 

 the bottom tow-net in Cawsand Bay, 



