Page:Transactions NZ Institute Volume 15.djvu/102

I find that my specimens differ from those described by Messrs. Bate and Westwood in one small point, which I had previously overlooked. In theirs the upper surface of the body "is tuberculated, each tubercle emitting a minute seta at its top." In my specimens the tubercles are not very well marked, and the setæ, though certainly very small, are perhaps rather too large to be called minute, as compared with the animal itself.

I do not, however, consider this difference sufficient to warrant its removal from the European species.

Body much depressed, almost flat. Both antennæ having some of the basal joints expanded, flat; outer antenna with a flagellum. Coxæ very largely developed. Last pair of pleopoda biramous, lamellar.

Plakarthrium typicum, sp. nov. Plate I., fig. 5.

First two joints of inner antenna much expanded, first sub-rectangular, second sub-triangular, bearing on its posterior border the third joint, which is small and not expanded and is followed by a very small joint bearing two or three auditory cilia. Outer antenna with peduncle of five joints; the first two small and cylindrical, the third expanded, triangular, fourth expanded, transverse, fifth cylindrical, followed by a slender many-jointed flagellum reaching to the posterior border of the third thoracic segment. Eyes small, placed in the centres of the two rounded lateral portions of the head. Head transverse, about twice as broad as long, entirely enclosed by the expanded joints of the antennæ and by the coxæ of the first thoracic segment. Thoracic segments sub-equal in length, the central ones being rather broader than the first and the last. Coxæ very large, lamellar, more than half as broad as their segments; coxa of last thoracic segment reaching nearly to the extremity of the last pair of pleopoda. First two pairs of legs slender, three following pairs short and stout, last two pairs slender, similar to the first two, all ending in strong curved claws. Abdomen sub-rectangular, showing indications of three segments, the last larger than the first two together; posterior border concave. Last pair of pleopoda apparently arising right at the posterior end of the abdomen, basal joint short, flat, about as long as broad, inner branch oblong, inner margin straight, outer branch broader, expanding distally.

Colour—light-reddish brown, with a few small scattered dots of a darker brown. Length about ⅕ of an inch.

Hab. Lyttelton Harbour. On stems of a brown seaweed, probably Ecklonia radiata.

I do not know where this peculiar Isopod should be placed. In some respects it is like Amphoroidea, but it differs very greatly from it in others. As yet I have only found it on one kind of seaweed, probably Ecklonia