1891.] MR. BOULENGER ON PROTOPTERUS ANNECTENS. 147 



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 thej are in any degree inherited. 



The species here called Glausilia 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. bideatata, Strom, 

 10 millim. long, and G. 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 fevf days ago Miss Catherine Hopley kindly informed me 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 oflF, 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-Ximh. My friend Prof. Howes, who has kindly made a prepa- 

 ration of the specimen, has ascertained that the supplementary rays 

 are fused together at the base by their proximal segments. 



A few years ago Albrecht ^ 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 



» Sitzungsb. Ak. Berl. 1886, p. 545, pi. vi. 



10* 



