122 On a Parasitic Copepod of the Clam. (February, 
an exhaustive account of the form ot the appendages. If a sec- 
ond species of the genus should be found, diagnostic marks will 
be readily obtainable from the figures. The anatomy of the soft 
parts appeared to agree so completely with Della Valle’s ac- 
count of Lichomolgus sarsii, that I abstain from any description 
thereof. 
There are two points of some interest which I have not referred 
to in the diagnosis. The mouth corresponds in position nearly 
to the notch of the labrum, and is situated between the points of 
the mandibles. Behind this point is a sort of vestibule bounded by 
the distal joints of the anterior maxillipedes, the dorsal wall of 
which is formed by the sternal surface between the basal joints of 
the mouth parts. A crescentic row of minute spines follows the 
curve of the maxillipedes, and two pointed chitinous processes 
project into the vestibule further back. These are connected with 
the chitinous framework surrounding the sockets of the mouth- 
parts. I have not had the opportunity of observing whether they 
play the part of teeth. They appear to me comparable to the 
lobes of the Metastoma (unterlippe) described by Claus! for 
Nereicola. A further agreement with that genus is the presence 
of a chitinous process which corresponds in position to the absent 
posterior maxillipede, and is no doubt a rudiment of that 
member. 
I have met with no trace of the sixth pair of limbs described 
by Della Valle as projecting from the anterior half of the genital 
segment in Lichomolgus and do not hesitate to reckon al! of 
the double genital segment to the abdomen. 
The presence of female Myicolz in the gill-tubes of a clam is 
readily detected by local swellings of the tube corresponding to 
the length of the parasites. With a needle they are readily freed, 
and swim about with considerable velocity considering that their 
legs have not been stretched since they were imprisoned in the 
gill. Iam unable to say by what channel they reach their rest- 
ing place. I have found some in the suprabranchial chambers, 
which would seem to indicate entry through the cloacal siphon, 
while I have found others, head upward, in the gill-tubes, which 
would appear to argue an entry, while still in the nauplius-stage, 
ole the inhalant siphon and the water-pores of the gill- 
plates. 
1 Zeit : wiss : Zool., XXV, p. 342, pl. XXII, fig. 21. 
