262 Proceedings of the Royal Physical Society. 



metrical, the posterior end was narrow, and the sides sloped 

 outwards (Fig. 9). Both horns were turned outwards, but were 

 generally of unequal length, leaving a wide opening between 

 them. A variety of this occurred once in which the left 

 horn was almost rudimentary, being very slightly turned out- 

 wards, while the right horn was of large size, curved first out- 

 wards, then turned anteriorly and inwards, so as to describe a 

 semicircle. 



There are so many slight variations in this species, that it 

 is rather difficult to fix upon a typical form of tubercle, conse- 

 quently the following description has not been made very 

 strictly, in order to leave a margin for slight variations. 

 Olfactory tubercle small, oblong, usually U-shaped. Pos- 

 terior end rounded or pointed, never wider than 

 the anterior end ; sides symmetrical, one sometimes 

 longer than the other. Aperture anterior, very vari- 

 able in width. Horns frequently unequal, usually 

 turned inwards. 



CORELLA PARALLELOGRAMMA, 0. F. MUUer. 



In this species the olfactory tubercle is small, and fairly 

 constant in form. Only a few variations were found, but one 

 or two of these were peculiar. The peri-tubercular area varies 

 in size, in some individuals only accommodating about one- 

 half of the tubercle, while in others it includes the whole 

 organ. There is usually a considerable space between the 

 top of the tubercle and the base of the tentacles. 



The olfactory tubercle is semicircular in outline, the 

 anterior end being broad and the posterior convex. In the 

 simplest form noticed, and the one that occurred most fre- 



Fig. 10. Fig. 11. 



quently, the organ is a simple curve, a semicircle, or a 

 crescent, with the horns directed anteriorly, diverging, not 



