816 PROF. G. C. BOURNE ON THE [Nov. 17, 



clextral coil of the spire and their shells are asymmetrical, in 

 general form somewhat like Haliotis. The same is the case with 

 iV. oiveniana Gray, from the W. Coast of A.frica, Fernando Po, 

 and Cape Palmas ; and thus it appears that the Neritinaj of rivers 

 running into the Indian and Pacific Oceans (but not of American 

 rivers on the Pacific slopes) have given rise to the limpet-like 

 fluviatile genus Septaria, whilst those of the Atlantic shores have 

 followed a different line of evolution and have in no case given rise 

 to Septaria forms. 



The genus Septaria Ferussac is commonly referred to in 

 zoological works as Navicella Lamarck, but Ferussac's name has 

 the priority and, according to all rales of zoological nomenclature, 

 ought to be adopted. It appears to be a characteristically fresh- 

 water genus, living on the roots of Nipa palms and other trees on 

 the banks of rivers in India, Mauritius, Bourbon, N. Australia, 

 and the Pacific Islands. The Heptarioi of the Mascarene Islands 

 and Madagascar aflfect the vicinity of waterfalls, and are found 

 adhering to stones out of the water but constantly wetted by 

 spray. Due allowance being made for the secondary symmetry 

 which they have acquired, the internal anatomy of individuals 

 of this genus closely I'esembles that of Nerita and the tropical 

 Neritinae. Little or nothing is recorded of the breeding-habits 

 and development of Septaria, but some specimens of S. hou.gain- 

 villei Recluz, a Fijian species in my possession, have egg-cases, 

 resembling those of Neritina JiiiviatiUs, attached to the shell, each 

 case containing a number of veliger larvae. 



No more than a passing mention can be made here of the 

 Titiscaniidse, of which Titiscania Bergh is the sole genus. It is 

 a slug-like marine form, probably widely distributed in the Indo- 

 Pacific seas, but hitherto recorded only from the Philippines and 

 Mauritius. It is a highly specialized member of the Neritacea, 

 with something of the form and habits of a Nudibranch. The 

 shell is lost, but the ctenidiumand mantle-cavity, though reduced, 

 remain. Bergh (2) has given an account of the anatomy of this 

 remarkable genus, from which it is evident that it is rightly 

 placed among the Neritacea, and probably near to Neritopsis^ 

 because of the absence of the median plate in the radula. There 

 are, however, many imperfections in Bergh's account of the 

 anatomy. Believing that the supra-intestinal nerve was absent 

 in Nerita, he failed to find it in Tltiscaniaj, and we are left in 

 doubt as to whether it is really present in the latter genus or not. 

 For similar reasons doubt must be thrown on his descrijjtion of 

 the heart with a single auricle, and his account of the generative 

 organs is so wanting in precision and detail that one can only 

 gather fi'om it that the accessory glands and ducts are complicated, 

 and may very possibly resemble those of Nerita. 



The remaining families of the Neritacea, the Helicinidfe, Pro- 

 serpinidee, a.nd Hydrocenidfe, are, as is well known, terrestrial 

 pulmonate forms, with the habits of snails. Their distribution 

 coincides on the whole closely with that of the tropical Keritm 



