380 W. G. Van Name — Bermuda Ascidians. 



Method of budding pallial (from wall of peribranchial cavity). 



The most important work dealing with the classification of the 

 members of this family is that of Michaelsen (12), previous classifi- 

 cations being- based upon the form of the colony or other features of 

 little significance. 



Michaelsen makes the structure of the reproductive organs the 

 chief character in distinguishing the genera. There is no doubt that 

 this is a great advance toward a natural system, and although his 

 innovations in the nomenclature may not be accepted in every 

 instance, he is amply justified in rejecting many of the older and 

 imperfectly characterized genera. 



I have not, however, been able to include either of the two Ber- 

 muda forms, here described, in any of Michaelsen's genera. Even if 

 only the structure of the reproductive organs be considered, his defi- 

 nitions would have to be modified (though in one case only slightly) 

 in order to receive them, and I believe that other differences in the 

 anatomy are of sufficient weight to justify the formation of new 

 genera. 



Michaelsenia, n. gen. 



Colony incrusting. Test thick and leathery. Both apertures four- 

 lobed. 



Branchial sac with folds and many internal longitudinal bars. 



Reproductive organs consist of a number of hermaphrodite poly- 

 carps of rounded or oval form, arranged in two rows (one each 

 side of the endostyle) on the ventral surface of the body, from which 

 they project into the* test as papilla? or tubercles, invested by an 

 evagination of the mantle, to the inner surface of which they are 

 attached. 



The form for which I have established this genus differs from the 

 genus Styelaoi the Simple Ascidians in only two essential characters: 

 first, in producing buds and forming colonies ; second, in the above 

 described arrangement of the sexual organs. In the character and 

 appearance of the test, apertures, tentacles, and branchial sac, as well 

 as in many minor particulars, the resemblance to Styela is very 

 striking. 



It is most closely related to Michaelsen's genus Polyzoa Lesson as 

 far as the structure of the reproductive organs is concerned, though 

 there the testis consists of but one vesicle in each polycarp. In 

 that genus, moreover, the branchial sac is without folds and has but 

 eight internal longitudinal bars on each side, and the form of the 

 colony is very different. 



