Tlie Actiiiiae of the Plate CoUection. 293 



a radius to develope. The aunexed diag-ram (Fig. B) shows the ar- 

 rangement on a portion of the disc where iio irreg-ularities occurred. 



DuERDEN has shoAvn that in several Discosomidae the arrange- 

 meiit of the disc tentacles bears a very definite relation to that of 

 the marginal tentacles and I share his hopefulness that something 

 may be accomplished toward Clearing up the relationships of the 

 various Stichodactyline species by a closer study of the arrangement 

 of the tentacles. Unfortnnately the literature contains little that 

 can be used in this connection for the Conjnacfidae, the fignres and 

 descriptions of C. viridis even not 3ielding data from which an ac- 

 curate determination of the relations of the tentacles may be made. 

 Indeed the only forms for which the data are sufflcient are the 

 two species of CoraUimorpJms and the species of Corynadis described 

 by Hertwig (1882), C. myrcia described by Duerden (1900) and 

 C. globulifera recently redescribed by Caklgren (1900). 



In Corynadis sp.? Hertwig. if I understand the description 

 aright, there are two cycles of marginal tentacles, a larger tentacle 

 as a rule alternating with a smaller one. The latter have no cor- 

 responding disc tentacles and are endocoelic in position, but the 

 former have disc tentacles on their radii, arranged so as to mark 

 out tliree sets. Thus, starting from a directive radius there are 

 flrst two disc tentacles, then on the next radius one situated more 

 peripherally than the outermost one of the first radius, then one on 

 the next situated on a line with the outermost tentacle of the ürst 

 radius, then again one corresponding with that of the second radius 

 and finaly a radius corresponding with the first one. The arrange- 

 ment may be expressed by the following formula, in which the disc 

 tentacles are indicated by numerals, the exocoelic marginal tentacles 

 by m and the endocoelic by M. 



M2 — m — Ml — m — Ml — m — Ml — in— M2 



In Corynadis myrcia the figure given by 

 Duerden seems to indicate that there are 

 no exocoelic marginal tentacles and the disc 

 tentacles are arranged in two alternating 

 sets (Fig. C), the formula being 



M3 — — Ml — — M3 



In C. globulifera Carlgren found a con- 

 siderable amount of irregularity, but the funda- 

 mental formula may probably be set down as Fig. C. 



