368 W. G. Van Name — Bermuda Ascidians. 



above mentioned, the colony is veiy soft and delicate. No spicules 

 are present. The test is often very transparent. 



The zooids have six lobed or nearly simple branchial apertures, 

 and simple atrial openings. 



The branchial sac has four rows of rather large stigmata. The 

 transverse vessels are muscular, and as in Leptoclinum there is a 

 muscle band along each side of the dorsal lamina. The bands unite 

 at the posterior end of the thorax, and are prolonged into a muscu- 

 lar and vascular process extending posteriorly and ventrally into 

 the common test. It ends bluntly and is much weaker and less con- 

 spicuous than in Leptoclinum. I have found it in all the species of 

 this genus described in this paper. 



The intestinal loop is twisted and generally bent so that its axis 

 lies about at right angles to that of the thorax. This brings the 

 reproductive organs, which lie on the left side of the abdomen, 

 under the intestinal loop. The stomach is oval and smooth-walled, 

 on the outside at least. 



There are two testes placed close together, forming as in Lepto- 

 clinum a conical mass, but the vas deferens does not coil about them. 



With the related Dlplosomoides Herdman, which has small stel- 

 late calcareous spicules, this genus is often made a separate family, 

 the Diplosomida?. 



Diplosoma macdonaldi Herdman. 



Diplosoma macdonaldi Herdman, Eeport Voy. Challenger, pt. xxxviii, p. 315. 

 Plate LIII. Figure 60. Plate LX. Figure 124. 



Colony large (50 m,D across) and rather thin, not exceeding 2 or 

 2.25 mm in thickness. Test nearly colorless and very transparent, 

 membranous on the surface. The cavities characteristic of the genus 

 are well developed, yet there is considerable test substance about 

 the zooids which adheres very firmly to their mantles and contains 

 here and there a few bladder cells. In addition to the small test 

 cells, there are large oval or slightly irregular cells which stain 

 deeply with plasma stains. 



The zooids are also nearly colorless except that the stomach and 

 more or less of the intestinal loop is yellow or orange. This fades 

 out in preserved specimens. The zooids are large for this family, 

 sometimes reaching 1.6 mm in length when straightened out and 

 expanded. The mantle muscles are but slightly developed and are 

 mostly transverse. 



