W. G. Van Name — Bermuda Ascidians. 301 



I liave not been able to count more than al)out a dozen stigmata 

 in a row on each side. None of the specimens have reproductive 

 organs in good condition. 



One colon}^ of this little species Avas collected in 1898. In 1901 

 two or three were obtained in Bailey's Bay and Harrington Sound. 

 One of the sisecimens grew on a bi'anching alga, the others incrusted 

 coral. 



Didemnum orbiculatum, n. sp. 



Plate LI. Figures 32 and 38. Plate LXI. Figures 137o and 128. 



This is a form in many respects intermediate between a true 

 Didemnum and a Leptodlmim, having the thin colony and abundant 

 si^icules characteristic of the latter, yet the large size of the spicules, 

 their form, and the appearance and pigmentation of the zooids show 

 it to be closely related to some of the species just described, and as I 

 have been able to distinguish but three rows of stigmata it seems 

 best to place it in this genus. 



The largest specimens found were 25 or 30™"' across, and about 

 2""° thick. 



It may be recognized at a glance by the peculiarity in the distri- 

 bution of the spicules alluded to in the analytical table above. 

 The sj)icules, which are of fair size (about .04'°'"), with rather 

 slender conical points, are abundantly and thickly disposed in the 

 test, yet not in such numbers as to give the colony the white, chalky 

 appearance of a Leptoclinnm, but leaving it a translucent grayish 

 Avhite. The zooids are placed very close together, and there being 

 but a thin layer of spicules over them, each branchial orifice appears 

 in the center of a more transparent circular area of about the diam- 

 eter of the thorax of the zooid. 



The zooids ai'e small (in contraction about V^^ long). They have 

 strong muscle bands in the mantle and conti'act badly in preserva- 

 tion. The mantle contains much dark pigment on the thorax, so that 

 that part of the body often appeal's quite uniformly blackish. 



This species is common and grows on the underside of stones near 

 low water in company with colonies of TieptocUnum, Diplosomoides 

 and Botrylloides at almost all suitable places along the shores of the 

 islands. I found it especially common at Long Bird Island and at 

 Waterloo, on Ca.stle Harbor, in April and May, 1901. Many of the 

 zooids then contained large eggs, but I did not observe well devel- 

 oped testes in anj^ of the numerous individuals examined. 



