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Show 712 MR. E. A. SMITH ON SHELLS FROM LAKE NYASSA. [Nov. 6, present, although never large; whilst in the two last-named birds, both from Africa, it is absent on both sides of the body. bucn being the case, it seems to m e highly probable that the relationship between Abdimia sphenorhyncha and Xenorhynchus senegalensis is more intimate than that between X. senegalensis and X. australis; and this view is favoured by their geographical distribution. The tendency of the ambiens muscle to vanish in certain ot the birds so closely allied as the Storks under consideration, in certain Psittaci, as well as in some of the Columbae, is one which our knowledge of their habits does not enable us to explain. It can have no relation to the habits or bulk of the species ; for this muscle is present in the Ostrich as well as in the smallest Cuckoo, whilst it is absent in the Cassowaries and the Passeres. The fact that it is not found in certain Storks makes its total loss in the Ardeidae less surprising than it would otherwise be. 6. O n the Shells of Lake Nyassa, and on a few Maxine Species from Mozambique. By E D G A R A. S M I T H . [Eeceived September 29, 1877.] (Plates LXXIV. & LXXV.) The British Museum has recently acquired a small series of shells collected by Mr. F. A. Simons at Lake Nyassa, and a few obtained by him at the mouth of the Macusi river, near Quilimane, on the east coast of Africa. Among the former are several very interesting though small species, which, as far as I have been able to ascertain, are undescribed. As complete lists of species from restricted localities are very useful, I have brought together all those which are known inhabitants of the lake. Fourteen, collected by Dr. Kirk, are all that have as yet been recorded; and now I am enabled to add eleven others to that number. Of these the Melania polymorpha is very remarkable, as showing the great variation to which some Melaniee are subject; and, indeed, I do not feel at all certain that the two forms, M. pupiformis and M. turritospira are not very abnormal growths of the same shell. I. LAKE-SHELLS. 1. MELANIA TUBERCULATA, Miiller. Hab. Lake Nyassa (Simons and Dr. Kirk). Four specimens of this variable species from the lake differ from the normal and usual form in having the whorls less convex. There is a narrow white zone at the top of the whorls next the suture ; and beneath a pale-olive epidermis the shell is semitransparent, whitish, and ornamented with series of minute red dots. The longitudinal ribs |