MOLLUSOA OF PLYMOUTH SOUND. 177 



N UDIBR ANCHI AT A 



(= OPISTHOBRANCHIA NON-PALLIATA, Lankester). 



Sub-order l-PYGOBRANCHIA, Gray. 



Family— BOmDlBM, Leach. 



Suh -family — Dokidid^ ceyptobranchiat^, Bergh. 



1. AechidoriS; Bergh. 



1. A. TUBERCULATA, Cuvier. 



Common among the rocks between tide-marks. As many as 

 thirty specimens were obtained on May 31st at Bovisand, north of 

 the pier. Spawn this year most abundant in March and April^ but 

 on account of the mildness of the winter and warmth of the spring*, 

 marine animals generally have been breeding earlier than usual. 

 On May 29th half-a-dozen specimens were obtained from the shore 

 at Batten, of which one was only three quarters of an inch long, and 

 several others were less than an inch and a half in length. The 

 spawning is prolonged throughout the summer. On August 2nd a 

 young individual was dredged in twenty fathoms off Rame Head, 

 one inch in length. Several large specimens have been met with 

 at various times ; the finest, which was five inches in length, was 

 obtained from the mouth of the Yealm on January 21st. It was 

 seen in a fathom of water from the boat's side by W. Roach, our 

 fisherman, and would have been in two feet of water at extreme ebb. 



This species usually feeds upon Halichondria panicea, a very 

 common littoral sponge, and"^ Giard (6) has noticed the general re- 

 semblance it bears in form and colour to its prey. It would be 

 more correct to say that it is protectively coloured in relation to its 

 surroundings ; see Herdman (13) for a very good case and for his 

 remarks upon it. Professor Stewart tells me that he once obtained 

 on the shore at Cremyll four or five individuals, apparently of this 

 species and at least two inches long-, from a mass of Hymeniacidon 

 sanguinea upon which they were feeding, and that, remarkably 

 enough, they were all bright red in colour. Possibly they were 

 examples of Alder and Hancock's species Archidoris jiammea, though 

 more than twice the size of their specimens. 



2. A. JoHNSTONi, A. and H. 



I have only seen one individual of this species, though Professor 

 Stewart tells me that in former days it was very plentiful. I obtained 



* More than fifteen years ago Giard remarked upon the deceptive appearance of this 

 species " au milieu des masses rougeatres des Amarouques qui couvrent le fond" (Arch. 

 Zool. Exp., i, 1872, pp. 553, 558.) 



NEW SERIES. VOL. I, NO. II. 12 



