260 Proceedings of the Royal Physical Society. 



shaped. Posterior end angular, sides unequal. Aper- 

 ture anterior, directed slightly to the left, not wide. 

 Horns rather short, always bent inwards, unsymmetri- 

 cally curved, the right overlapping the left. 



AsciDiA SCABRA, O. F. Miiller. 



The peri-tubercular area is here moderately deep, and is 

 usually symmetrical. It accommodates from three-fourths to 

 the whole of the tubercle, which is thus kept at a considerable 

 distance from the base of the tentacles. 



The olfactory tubercle is simple. In its usual form it is 

 oval, with the posterior end rounded, and the horns sloping 

 inwards towards each other, leaving an aperture of variable 

 width between them. 



Two marked variations occurred in the specimens I have 

 examined. In the first the general shape of the tubercle 

 was normal, but at the anterior end the extremities of the 

 horns were both bent sharply to the right and posteriorly, 

 so that one horn turned inwards and the other outwards. 

 The left side of the tubercle also was slightly longer than 

 the right, consequently the left horn occupied a position 

 anterior to the other. This tubercle was rather larger than 

 is usual in the species. 



Fig. 7. 



The other variation was caused by the left horn being 

 greatly developed, while the right was quite rudimentary 

 (Fig. 7). At the anterior end the two sides approach and 

 almost meet, as in the typical form, then the left horn bends 

 anteriorly, and takes a wide sweep outwards, describing about 

 three-fourths of a circle. If the right side was still more 

 rudimentary, and the left horn more developed, this variety 

 would easily approach the sigmoid form described in Ascidia 

 virgi^iea. 



