From the kindness of Professor Owen, Mr. Gray, and Mr. Cuming, I have been enabled to examine six specimens of this species; and on two of them I found Complemental males. They were attached in the same position as in _S. Peronii_; namely, beneath the adductor muscle, in the fold between the scuta, so as to be protected by the latter when closed. This parasite is six-valved, and has a close general resemblance with that of _S. Peronii_, but differs in very many points of detail. It is represented of the natural size at _á_ fig. 4. The capitulum is 43/1000ths of an inch, measured across the scuta and terga; and the same measured from the base of the carina to the top of the capitulum; hence it is broader, by a quarter of the above measurement, and considerably higher than the male of _S. Peronii_. From the capitulum being higher, that is, not so much truncated, the orifice is placed more obliquely. The membrane connecting the valves is finely villose, and is besides furnished with spines, conspicuously thicker and longer than those on the male _S. Peronii_. The scuta and terga are much more elongated, a scutum being here 35/1000ths of an inch in length. The carina descends only just below the basal points of the terga, instead of far below them. The rostrum is a little broader and more arched than the carina; it is 2/1000ths in length, and therefore more than two thirds of the length of the carina, the latter being 28/1000ths of an inch from the apex to the basal margin. The primordial valves, with the usual hexagonal tissue, are seated on the tips of the scuta, terga, and carina, but not on the rostrum; so that these valves follow the same law of development, as in the ordinary and hermaphrodite form of Scalpellum. The scuta (_a_, fig. 4, greatly enlarged), the terga (_b_), and carina (_c_) of the male, resemble the same valves in the hermaphrodite, much more closely than do these valves in the male and hermaphrodite _S. Peronii_. The rostrum has not its basal margin hollowed out, and is very much larger relatively to the carina, than in the hermaphrodite. The large relative size of the rostrum in the complemental male both of this species and of _S. Peronii_, is a remarkable character, which I can in no way account for. The peduncle is narrow and short, but in a different degree in the two specimens examined. It is naked. The prehensile antennæ were not in a good state of preservation: the disc is narrower than the basal segment, and only slightly pointed, in which important respect it differs from the same part in the foregoing species; at its distal end, rather on the inner side, there are two or three spines, apparently in place of the excessively minute hairs, which are found at the same spot in some or in all the other species of Scalpellum, and in Ibla: similar strong spines occur in Pollicipes. Unfortunately, for the sake of comparison, I was not able to find the prehensile antennæ in the hermaphrodite _S. villosum_.