1885.] On a Parasitic Copepod of the Clam. 121 
pedes in the female. In the proportionate size of the thoracic 
segments, the position of the mouth and the conformation of the 
natatory feet, it approaches on thé other hand the Lichomolgide, 
and especially those forms already found in Lamellibranchiata.- 
The dimorphism of the cephalothorax, which is more striking 
than in any of the allied genera, is no doubt to be attributed to 
the cylindrical form of the water-tubes of the gills in which the 
females live. 
If Lichomolgus and the Saphirinidz be merged into the family 
Coryceidz, as seems the most natural arrangement (cf. Claus, 
Lehrbuch der Zoologie, p. 554; and Brady, Zoology of the 
Challenger expedition, Vol. vit, p. 109, e¢ seg.), then the exist- 
ence of the above described genus renders imperative the accept- 
ance of Della Valle’s proposal to include Ergasilus in the same 
family (Z c. p. 83). So extended, the family of the Coryceide 
would embrace some free and some semiparasitic forms, some 
parasites of pelagic animals, and a few whose females at least are 
constant parasites of Pisces, Mollusca, Vermes and Ccelenterata. 
The following description of the species will, with the help of 
the figures, serve to elucidate its most important characteristics: 
Myicola metisiensis, n. sp. Q 3™™ long, of which 1™ belongs to the abdomen, 
inclusive of the furca. © 1.75™™" and less, First four free thoracic segments of 9 
subequal, broader than long, the fifth smaller than the first abdominal segment 
and chiefly developed dorsally, Thoracic segments of (j' gradually decreasing in 
breadth from before backwards. Double genital segments of Q abdomen nearly as 
long as remaining three segments. The posterior borders of the genital and two fol- 
lowing abdominal segments of <j EES Furcal segments as long as two 
ast abdominal; setze six, of which three are apical and one subapical. Rostru 
kidi daad. anterior antennæ as long as the head, the first, second and fifth joints 
the longest. Posterior antennæ directed downwards; shorter than the anterior. 
Labrum with lateral borders denticulated, and posterior border emarginate. Mandi- 
ble with two setose lobes and two setose filaments. Maxilla with three setæ, of 
which the mesal is longest. Two basal joints of anterior maxillipede tumid, with 
two converging oblique patches of spines, the distal joint with a strong seta and ter- 
minating in two curved setose filaments of which the slenderer is attached like a 
palp. Posterior maxillipede of ¢‘ with basal joint denticulated. Basal joint of Ist 
pair of natatory feet with a row of strong spines on the ventral surface, decreasing 
in strength on the 2d and 3d pairs, and absent on 4th; 5th pair uniramous, with 
three joints, the two proximal of which carry each a distal seta, while the distal 
two apical sete and a subapical group of spines. 
Egg-sacs two, cylindrical, 1™™" X 0.5™™ 
Spermatophores subpyriform, 0.2™™ X O.1™™, 
© parasitic in the gill-tubes of Mya arenaria, at Little Metis, Quebec, Canada. 
¢ free in the mantle‘cavity of Mya. 
I have not thought it necessary in the above diagnosis to give 
