SPECIES OF CEPHALODISCUS. 7 



may be but short, thick lips to the peristomial tube. Most important of all, however, 

 is the isolation of the polypides of certain species in tubular spaces in the tubarium, 

 in contrast with the occurrence of all the polypides of the colony in one continuous 

 cavity in other species. 



Harmer, on p. 6 of his monograph (10), gives a list of the generic characters of 

 Cephalodiscus ; but while attaching the name of M'Intosh as the author of the 

 genus to the name Cephalodiscus at the head of the paragraph, he alters the diagnosis 

 of that author by describing the tubarium as " with a continuous cavity or with 

 a separate cavity for each zooid." Until the discovery of C. levinseni it was not 

 known that any forms of Cephalodiscus existed in which the polypides had separate 

 tubes. The presence of (an average of) fourteen plumes in the polypides of 

 C. nigrescens, and the discovery that in both C. nigrescens and C. hodgsoni 

 hermaphrodite individuals occur, necessitate further alterations in the diagnosis 

 given by Harmer (10, p. 6). 



The isolation of the polypides in separate tubes within the common test is 

 clearly a feature of great systematic importance, and for the inclusion of species of 

 Cephalodiscus in which the polypides are so isolated Professor Ray Lankester has 

 been good enough to suggest the sub-generic name Idiothecia*. So far as our 

 present knowledge goes there are three such species, viz., C. levinseni (text-fig. 3), 

 C. nigrescens (plate l), and an undescribed species obtained by Dr. Gilchrist in the 

 Cape Seas. The remaining species of Cephalodiscus, in which the polypides are 

 more social and live together in the same edifice, namely, the type species C. 

 dodecalophus (text-fig. 4), and the recently discovered species C. gracilis (text-fig. 5), 

 C. sibogae (text-fig. 2), and C. hodgsoni (fig. 1, plate 2), are included in the sub-genus 

 for which Professor Lankester proposes the name Demiothecia^. Dr. Andersson's 

 note (1) is not sufficiently detailed to enable one to judge whether the Falkland 

 Islands specimens belong to C. dodecalophus, as that author suggests, or not. 



REVIEW OF THE SIX SPECIES OF CEPHALODISCUS. 



Genus Cephalodiscus. Polypides secreting a tubarium of gelatinous appearance, 

 formed of superimposed lamellae, and with ostia upon the surface. Polypides with 

 buccal shield, collar, and trunk. Shield with pedicle arising from middle of upper 

 surface, hollow, the cavity opening typically J by two small pores (proboscis pores) 

 on the dorsal surface. Collar with special paired division of coelom, opening to 

 exterior on each side by a canal (collar canal) near the gill-slit ; collar produced 



* From "Sior, one's own, personal, private, and 6^, a case, box, vault. 



f From Sr]fj.ws, belonging to the commonwealth, and 6f)Krj, a case, box, vault. 



t Proboscis pores, gill-slits, and post-oral lamella have not been recognised in the reduced males of 

 C. sibogae (10, p. 6), but the neuter individuals of that species conform with the generic diagnosis in these 

 respects. 



