1891.] MR. E. A. SMITH ON SHKLLS FROM ADEN. 391 



use to those who possess shells from this locality and are desirous of 

 identifying them. 



Before concluding these prefatory remarks I have some observations 

 to make respectjng the list of species which, according to Mr. Cooke, 

 are " common to the Mediterranean and the Red Sea " '. Examples 

 of the seventeen species he enumerates were collected in the Gulf of 

 Suez by the late Robert Mac Andrew in the early part of the year 

 186y, some months before the opening of the Canal. It is important 

 to note this as showing that their establishment in the Red Sea was 

 not of recent date. Before expressing any opinion with regard to 

 the accuracy of some of Mr. Cooke's identifications, it was necessary 

 for me to study the specimens tlieniselves, and consequently I 

 applied to Dr. Sharp of the Cambridge Museum, where the Mac- 

 Andrew collection is preserved, and I have to acknowledge his 

 kindness in forwarding all the specimens I required, and I have 

 also to tiiank Mr. Cooke for kindly looking them out for 

 transmission. 



The following is the result of my examination : — 



1. Cerithium (Pirenella) mammillatum, Risso. 

 (= cailluudi. Pot. & Mich.) 



Nearly all the Suez specimens, which may be referred to a strongly 

 marked variety of this sj)ecies, liave a peculiar facies. They have 

 two distinct rows of granules on the upper wiioris, wliereas in 

 Mediterranean specimens thire are mostly three or more, and in 

 these the granules are smaller than in the Red-Sea specimens. In 

 the Museum we have three specimens from Bonibay ^ which are 

 more like the Mediterranean form than that from Suez. 



In discussing the marine fauna of any particular sea, it is hardly 

 correct to include the genera Cerithidea and Leuconia, the former an 

 estuarine form and the latter an amphibious Pulmonate. Now the 

 distribution of some of the>e estuarine species is most remarkable, 

 and so unaccountable, that I think the occurrence of two forms in 

 some parts of the Mediterranean and the Red Sea hardly bears 

 upon the subject of distribution in question. An instance of this 

 unaccountable distribution has lately come to my notice which may 

 fittingly be recorded here : I refer to Neritina crepidularia. This 

 unmi.-takable species is known from the mouth of the Ganges, from 

 Pondicherry, Tranquebar, Ceylon, Mergui, Singapore, the Dutch 

 Indian Islands, Philippines, Japan, Persian Gulf, and lastly from the 

 Gold Coast, West Africa, where living specimens were collected by 

 Mr. R. Austen Freeman and presented to the British Museum. 



2. Emarginula elongata, Costa. 



Tlie specimen kindly sent me for inspection I certainly consider 

 distinct from the above sfiecies. It bears a close resemblance to it 

 in general appearance, and without close examination one would not 



^ Ann. Mag. Nat. Hist. 1886, vol. xviii. p. 394. 



* Cerithidea homhayana, Sowerby, Con. Icon. sp. 24. Badly described and 

 figured. 



