278 STUDIES ON TUNICATA, 



If, as Herdman* has suggested, Aurantium is a group of 

 insufficient importance to warrant its separation from Polyclinumy 

 then it is only necessar}^ to modify his dichotomous key(/.c.,p.616) 

 to the genera of the PoLYCLiNiDiE as indicated below, to make a 

 place for the new genus. 



g ( Both gonads in the postabdomen Polydinum, 



1 Ovary in the atrial cavity, testes in the postabdomen Sidneioides. 



SiDNEIOIDES TAMARAMiE, sp.nOV. 



(Plates XXV., fig.9: xxvi., tigs.1-6). 



External appeara7ice. — The colony consists of many separate, 

 shortl}^ pedunculated lobes closely packed together to form a bun- 

 shaped, or hemispherical ascidiarium. The peduncles of the 

 individual lobes are all united to a flat basal, stolonial expansion 

 which, in turn, is attached to a substratum of rock and 

 barnacles. This stolonial basis is only about one-half the 

 diameter of the colony, so that the lobes radiate as from a com- 

 mon centre. The colour of the ascidiarium is dull grey, due to 

 the presence of small, densely packed, incrusting sand-grains 

 imbedded on the surface of the test. The distal surface of each 

 lobe is flat, and bears round its edge a slightly prominent ridge, 

 and towards its centre, one, two or three fairly prominent papillae, 

 the orifices of as many cloacal chambers. The largest colony of 

 normal growth had a maximum length of 40 mm., and diameter 

 of 60 mm. (Plate xxvi., figs. 5-6). The ascidiarium above described 

 is such as grows on a flat surface; those growing in confined rock 

 crevices adapt themselves to the irregularities of their situation 

 and assume very various shapes. 



The ascidiozooids (Plate xxv., fig.9) are all arranged vertical 

 to the free surface, and, therefore, like the lobes, radiate as from 

 a centre; they present the tripartite division of the body charac- 

 teristic of the family. The total length varies from 17-23 

 millimetres. The relative proportions of thorax to abdomen to 

 postabdomen are approximately 13:9:9. The diameter of the 



* Herdman, Journ. Linn. Soc. xxii,, 1891, p.618. 



