973 REPORT OF THE COMMISSIONER OF FISH AND FISHERIES. 
Fam. CYSTODISCIDZ Gurley, 1893. 
Bull. U. S. Fish Com. for 1891, x1, pp. 412-13; ib., Braun, 1894, Centralbl. f. 
Bakt. u. Parasitenkde, Xv, p. 87. 
Definition —Phenocystes whose spores possess antero-posterior and 
bilateral symmetry; 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 taxo- 
nomic necessity) approximated Thélohan’s genus Spheromyxa. It is 
characterized, Thélohan 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 Myxidiwm or to Cystodiscus. Between the last two, the 
presence of a membrane around the myxosporidium and especially the 
bivalve structure of the spore would seem (at a taxonomic guess) rather 
to approximate Spheromyxa to Cystodiscus. 
It may be frankly admitted that, as at present composed, this family 
is somewhat unsatisfactory 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 now know (excluding Mywxidium ? sp.102, about whichhardly 
any data exist) 5 species: Cystodiscus immersus, Cystodiscus ?? diploxys, 
Spheromyxa balbianii, Myxidium lieberkiihnii, Myxidiwum ? ineurvatum. 
Of these M. lieberkiihnit presents a sufficiently distinct group of char- 
acters to warrantits delimitation as the type of a family. The other 4 
species 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 Mywxidium ? 
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 planes and the orientation 
of the valve-junction plane. I suspect the future will separate generic- 
ally C. ?? diploxys from C. immersus, the former appearing to have the 
valve-junection 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 Sphwromyxa are so dubious, 
the present provisional arrangement is probably preferable to another 
new genus, and perhaps a family. 
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