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Show 1891.] MR. BOULENGER ON PROTOPTERUS ANNECTENS. 14/ cause of that very common condition among the latter known as decollation. Is it not therefore possible that something of the kind may occur in the case of those small examples of Clausilia rugosa one often finds coated with a green algoid growth? The destruction caused by the alga would seem in this case to be of a very gradual character, not preventing the growth of the shell, but tending to make it small and on the whole less well-formed. If this explanation is correct, the peculiarities of these small forms are clearly somatogenic, and it would be a matter of interest to ascertain whether they are in any degree inherited. The species here called Clausilia rugosa has been divided by some authors into two or more, and the characters given for the supposed distinct species are often such as we have just noted above. Moquin- Tandon (1855) described C. perversa, which somewhat resembles our small form, and C. nigricans, which in the form of the aperture is like our larger one. Westerlund (1884) gave C. bidentata, Strom, 10 millim. long, and C. rugosa, Drap., 12 millim. long; and these are just the respective dimensions of our two forms. It thus appears that, although these specimens do not prove the specific identity of these and other segregates from C. rugosa, they show that some of the characters relied upon to distinguish them are probably of no specific importance. Mr. Boulenger exhibited the renewed left pectoral limb of a Protopterus annectens, living in the Society's Gardens, and made the following remarks :- A few days ago Miss Catherine Hopley kindly informed m e that one of the Protopteri now living in the Society's Gardens, after having had its left pectoral limb nibbled off by one of its companions about three months ago (as she had been informed by the keeper of the Reptile-house), had reproduced the said limb in a trifid condition. Fearing that so interesting an object might be lost by being again bitten off, I removed the reproduced trifid portion of the limb, which I now exhibit. The limb was bitten off about two-thirds of an inch from its base, and on being regenerated presented, in addition to the prolongation of the longitudinal axis with its series of mesomeres, two preaxial or dorsal branches, similar to, but shorter and more slender than, the axial; these additional branches are, like the axial, divided into cartilaginous segments, comparable to the parameres of the Cera-todus- limb. M y friend Prof. Howes, who has kindly made a preparation of the specimen, has ascertained that the supplementary rays are fused together at the base by their proximal segments. A few years ago Albrecht1 described and figured a Protopterus with a bifid right fore limb, remarking that its condition might be regarded as giving support to Goette's and Wiedersheim's theory of the evolution of the pentadactyle limb. The specimen now noticed 1 Sitzungsb. Ak. Berl. 1886, p. 545, pi. vi. 10* |