62 W. G. RIDEWOOD. 



the posterior lobe grows backward and downward ; it is thinner than the anterior 

 part of the shield, and maintains this relation throughout life. 



By the time the shield is so far differentiated as to possess a stalk or pedicle 

 attached to the middle of its dorsal surface, the " l>ody " or metasome is pear- 

 shaped, and a second pair (fig. 56), and third, and fourth (fig. 57) pairs of plume-axes 

 make their appearance. The bud is at this time capable of remarkable change of 

 form, and an eight-plume bud may show a long "body" and stalk, and a cupped 

 shield with an obvious pedicle (fig. 58), or, more usually, a flattened shield, 

 attached at its middle, but with no clear pedicle, and a short and wrinkled " body " 

 and stalk (fig. 57). As a rule, buds that have reached the same stage of 

 development, so far as can be judged by the number of plumes present, are of 

 approximately the same size, but it is to be noted that the eight-plume bud shown 

 in fig. 58 is exceptionally large. 



The red line of the buccal shield begins to appear at aljout the stage when 

 the fourth pair of plume-axes are hemispherical knobs only, or are losing their 

 hemispherical shape and are becoming elongated (text-fig. 17, B, p. 54). 



SUMMARY OF RESULTS. 



1. A new species of Cephalodiscus {C. hodgsoni) is placed on record (p. 3), 

 and descriptions are given of the two species obtained by the ' Discovery,' namely, 

 C. nigrescens and C. hodgvonl (pp. 20-49 and pp. 49-62). 



2. A new sub-generic name Id'wthecla is given for the inclusion of those species 

 of Cephalodiscus {e.g. C. nigrescens and C. levinseni) in which the polypides reside 

 in separate tubular cavities in the tu1)arium (p. 7), and the sub-generic name 

 Deiuioiliecia for those species in which the polypides live together in the same cavity. 



3. A review is given of the six recorded species of Cephalodiscus, namely, 

 dodecalophus, hodgsoni, gracilis, sibogae, nigrescens and levinseni (pp. 7-11), also a key 

 to the identification of these (pp. 11-12). 



4. Since the tubes of the tubarium of C. nigrescens are entirely separated and 

 show no signs of having been continuous at an earlier stage of development, a 

 suggestion is offered as to the behaviour of the polypides in the building up of the 

 tuljarium (p. 23). 



5. Descriptions and semi-diagrammatic figures are given of sections of the 

 polypides of C. nigrescens taken through structures of particular interest (pp. 34-41). 



6. The " problematical body " of Harmer, supposed by that author to consist 

 of lamellae, probably of a muscular nature, is shown in the case of C. nigrescens 

 to be formed, not of lamellae, 1)ut of obliquely interlacing cross-striped muscle 

 fibres (pp. 41-43). 



7. In both of the new species obtained by the ' Discovery ' there are 

 hermaphrodite individuals, with one ovary and one testis, as well as males and 



