278 REPORT OF THE COMMISSIONER OF FISH AND FISHERIES. 

 Fam. CYSTODISCID^ Gurley, 1893. 



Bull. U. S. Fish Com. for 1801, xi, pp. 412-13; ih., Brann, 1894, Centralbl. f. 

 Bakt. n. Parasiteiikde, xv, p. 87. 



Definition. — Pluoiocystes whose spores possess antero-posterior and 

 bilateral syninietry; capsules in 2 groups situated at the (anterior and 

 posterior) ends; a bivalve shell, the plane of junction of whose valves 

 is perpendicular to the longitudinal plane; condition of sporoplasm 

 unknown; type genus Cystodiscus. 



To the family as thus defined, I have provisionally (by way of tuxo- 

 Bomic necessity) approximated Thelohan's genus Splucromyxa. It is 

 characterized, Th^lohan says, by the structure of the spores, especially 

 by the form of the filaments and their disposition in the capsule. In 

 the absence of figures, the orientation of the spore, upon which classi- 

 fication must be based, is uncertain. The double grouping of the cap- 

 sules necessitates the approximation (at least among known genera) 

 of this genus to Myxidiiim or to Cystodincus. Between the last two. the 

 presence of a membrane around the myxosporidium and especially the 

 bivalve structure of the spore would sfcm (atataxonomic guess) rather 

 to approximate Si)hceromyxa to Cystodiscus. 



It maybe frankly admitted that, as at present composed, this family 

 is somewhat unsatismctory and must be held subject to revision, prob- 

 ably in the direction of elision. For of the species with the capsules in 

 2 groups we nowknow [exclndwg Myxidiiim f sp. 102, about which hardly 

 any data exist) 5 species : Cystodiscus immcrsus, Cystodiscus ff diploxys, 

 Spluvromyxa balbianii, Myxidium lieberJciihnii, Myxidium ? Incurvatum. 

 Of these M. UeberMlhnii presents a sufifieiently distinct group of char- 

 acters to warrant its delimitation as I he type of a family. The other 4 

 si^ccies then agree in two very important characters, viz: 



1. Arrangement of capsules in 2 groups. 



2. Presence of a bivalve shell. 



Further than this, however, our analysis can not, for want of data, 

 be at present safely pushed. Indeed, I have even left Myxidium f 

 incurvatum under Myxidium (where in all probability it does not 

 belong) rather than place it elsewhere at random. Obviously the next 

 step is the determination of the 3 symmetry i)lanes and the orientation 

 of the valve-junction plane. I suspect the future will separate generic- 

 ally C. t? diploxys from C. immersus, the former appearing to have tlie 

 valve-junction plane parallel and the latter to have it perpendicular 

 to the longitudinal plane. In the present uncertainty, however, espe- 

 cially as long as the symmetry-relations of Splmromyxa are so dubious, 

 the present provisional arrangement is j)robably preferable to another 

 new genus, and perhaps a family. 



