374 W. G. Van Name — Bermuda Ascidians. 



The form of the systems is not a veiy satisfactory character on 

 which to base a group of full generic rank, and various writers have 

 attempted to attribute to Botri/lloides additional distinguishing 

 characters based on the cylindrical form and upright position of the 

 zooids in the colony, as w^ell as on the position of the atrial siphon, 

 which in this genus is said to be placed near the anterior end, while 

 in Botryllas the zooids are of more ovate form, lie horizontally in 

 the colony and have their apertures more widely separated. 



These characters are of very little significance. The form and 

 position of the zooids is chiefly dependent on the closeness with 

 which they are crowded together in the colony, while the position, 

 form, and length of the atrial siphon depend entirely on the relation 

 of the zooids to the common cloaca, or the branch of the same into 

 which the zooid discharges, and to which, of course, the atrial siphon 

 must reach. Great variations in these characters may occur within 

 the limits of a single colou}^, and they are not even of specific value. 

 The genus must be separated from Botryllas, if separated at all, on 

 the strength of its complex branching systems. 



As with the Botryllidae of other parts of the world, the Bermuda 

 forms are very variable, both in color and shape, and in the arrange- 

 ment of the zooids in the colony, and it is diflicult to determine how 

 many distinct species are really represented. The differences between 

 the extremes of variation ^re ample for regarding them as distinct 

 species. Yet so many colonies with characters intermediate between 

 those of the types described below are to be met with in a large 

 series of specimens, that the writer does not feel justified in giving 

 the new forms which are here described full specific rank, and in 

 this paper all the Bermuda forms, distinct from each other as the 

 typical examjjles are, will be treated as subspecies of B. nigrum 

 Herdman. 



Botrylloid.es nigrum Herdman. 



Botrylloides nigrum Herdman, Eeport Voy. Challenger, pt. xxxviii, p. 50. 

 Botrylloides nigrum Herdman, Sluiter, Tunioaten von Sltd-Afrika, Zool., 

 Jahrbiicher, vol. 11, 1897. 



Plate LIII. Figure 54. Plate LXI. Figure 125. 



To this species, described by Herdman from specimens taken 

 "near the island of Bermuda," most of the examples obtained can be 

 referred without much question. It is a common species and was 

 found both in 1898 and 1901, and also by Prof. Goode in 1876. 



