•228 
ALFRED GIARD. 
In the month of June last I twice found the two species 
of Orthonectida associated in the same specimen of an 
Ophiurid. 
It has appeared to me as though the Orthonectida were 
more common in the autumn than at any other season. But 
this perhaps depends on the fact that I had been able to 
give more attention then to my researches than during the 
academical session. 
III. — Anatomy of Rhopalura ophiocom^. 
Nothing is easier than, with aid of fine needles, to separate 
the whole dorsal region of Ophiocomma from the ventral disc 
formed by the buccal plates and the arms. The animal 
deprived of its dorsal cupola, and consequently of its diges- 
tive and reproductive organs, lives nevertheless several days, 
walks, and conducts itself generally as though no injury had 
occurred to it. 
In tearing open the dorsal cupola, in order to force out the 
embryos, the glass slip on which the operation is being con- 
ducted is sometimes seen to be covered by small white 
flakes, which, on examination with a low power of the 
microscope, are seen to be animated by a rapid movement of 
translation in a straight line, which is highly characteristic. 
This movement, common to all the species of this group, 
has led me to give to these organisms the name of Ortho- 
nectida. These agile little animals resemble large ciliated 
infusoria of a porcellanous aspect and a generally cylindrical 
form. A certain number, however, have a somewhat shorter 
form, irregularly ovoid, and move more slowly. 
In the one form or the other they are simple Planulce, 
nov. sp.), which is found even on the arms of young individuals still 
enclosed in the maternal incubatory pouch (very common). 
2. An Urceolaria {Ur. ophiocomce., nov. sp.), also very common. 
3. A copepod crustacean of the family of the Ergasillidae, or rather 
of a distinct family comprising the annelidocolous species. This crus- 
tacean, which is broad and provided with hooked limbs, attaches itself 
to the arm of the Ophiurid between the bristles. It recalls the form of 
the crab-louse. By a very natural association, I name it Phthiriopsis 
and I dedicate this parasite of the star-fishes to M. Emile Blan- 
chard, who teaches at the Museum of Paris the history of the Arthro- 
poda. The Phthiriopsis is very rare. 
4. A curious little annelid of the genus Sphserodorum, which presents 
the same relations to Ophiocoma which Chlorhema Dujardinii does to 
Psammechinus miliaris. 1 shall call it Spht^rodorum Gi'eejii, dedicating it 
to the learned Professor of the University of Marburg. About one 
Ophiurid in fifteen harbours a Sphcerodorum. 
All these parasites of Ophiocoma will be studied in detail in a special 
memoir. 
