74 UNITED STATES NATIONAL MUSEUM BULLETIN 251 



The spicules of B. {D.) apersum are, however, a little larger (16-25ju,) 

 than those of the present new species, although the shape of these two 

 species is quite similar. Moreover, the existence of the short common 

 cloacal siphon and the lacunae system extraordinarily developed in 

 the present new species is quite unique ; and the species is named for 

 the first of these characteristics. 



25. Didemnum (Didemnum) dorotubii, new name 



Figure 24a 



Hypurgon fuscum Oka, 1931c, p. 287, fig. 1. 



Didemnum (Didemnvtn) fuscum Tokioka, 1953a, p. 192, pi. 12, figs. 1-10. 

 Non Didemnum fuscum Sluiter, 1900, p. 52. 



MATERIAL EXAMINED 



China : Probably vicinity of Amoy, T. Y. Chen, Univ. of Amoy, sta. 2, no other 

 data available; received October 12, 1932. One fragment (USNM 11534), from 

 surface of solitary ascidian Microcosmus exaspcratus (Heller) (USNM 11528). 



Philippine Islands : Small Sibago Island ; W. R. Taylor, sta. 7. One colony 

 encrusting an alcyonarian coral (USNM 11667). — Baliwasan ; W. R. Taylor, sta. 

 10. Eight colonies encrusting an alcyonarian coral (USNM 11657) ; many colonies 

 (USNM 11656). 



Description. — Examined were a single encrusted colony, 15 mm. X 

 15 mm. in extent and 1.5 mm. in thickness, from Amoy, Chma, and 

 many colonies encrusting the alcyonarian colonies or leaves of Hal- 

 imeda from the Philippine waters, the largest one of the latter is 24 

 mm. X 17 mm. in extent and 1-2 mm. in thickness. 



Test translucent, devoid of spicules (Chinese specimen) or contain- 

 ing spicules somewhat densely around the branchial apertures but ex- 

 tremely sparsely in other parts of the colony (Philippine specimens). 

 Test packed very densely with fecal pellets, except the area around 

 the branchial aperture above respective zooids, thus the whole colony 

 is colored with a mudlike yellowish-brown tint. Spicules small, 20- 

 25/x in diameter, of the candiduin-type, and with very many fine rays. 

 Some of spicules found in a dissolving state. Atrial aperture of zooids 

 wide, four stigmatal rows, one testicular follicle, proximal part of vas 

 deferens coils more than five times. 



Structure of larva resembles closely that of Didemnum (Didemnum) 

 moseleyi (Ilerdman). Trunk is 380-400/^ in length, with four pairs 

 of ampullae; two pigment flecks of sensory organ arranged antero- 

 posteriorly. 



Remarks. — The specific name fuscum in the genus DidenvnuTn is 

 preoccupied by Sluiter for Didemnum fuscum, new species (1909, 

 Sihoga-Y^'^^Q.di., Monogr. 56b, p. 52). As there is no reference to the 

 existence of the atrial languot in Sluiter's descriptions, his si)ccies 

 seems to belong to the subgenus Didemnum. Consequently the specific 

 name of Hypurgon fuscum cannot be retained when this species is 



