TRANSACTIONS OF THE SECTIONS. 117 



first established instance of the occurrence of Nipharffi in England, was Mr. West- 

 wood's discovery at Maidenhead, Berkshire, of a well containing numbers of JS r . 

 amtilex. They have more recently been obtained from Corsbam and Warminster, 

 Wiltshire, and also from Ringwood, on the borders of the New Forest, Hampshire, 

 Crangonyx subterrancus has occurred at the two latter places, but not at the first 

 named. Niphargus fontanus is found at both Corsham and Ring-wood, but with a 

 difference iu the shape of the gnathopoda and posterior pleopoda, amounting: to a pro- 

 bably distinct variety, if not species. The form of the gnathopoda, or hands, is 

 worthy of attention, being each armed with a moveable claw of large size, forming 

 a prehensile organ of great power. N. fontanus is also possessed of small, yellow 

 eyes, which distinguish it in a very marked way from the allied species (of the 

 genus Gammarus) found on the Continent. Every member of the subterranean 

 Fauna hitherto found has been destitute of eyesight. The movements of Niphargi, 

 when kept in captivity, are interesting to observe ; but Mr. llogan states that he 

 has found great difficulty in preserving tliem alive. The longest period during which 

 even the strongest specimens survived its capture was three weeks. The average 

 temperature of the water in which Niphargus and Crangonyx are found is about 

 50° Fahr., and they seem to propagate in recently-formed wells as freely as in old 

 ones. In no case have any species of this family been found, either in this country or 

 abroad, in open wells or other than artificial ones, — pumps, in fact. They are found 

 at all seasons of the year, but most abundantly towards the end of the autumn. The 

 largest size known among the English species (that of X. fontanus) hardly exceeds 

 half an inch. Mr. llogan hoped that more extended observations would be made 

 in Great Britain on this interesting family of Crustacea, as their economy and struc- 

 ture are as yet very imperfectly known, and an accurate examination would be sure 

 to reward the investigator with results at least as interesting as those already 

 obtained regarding their allies by Continental naturalists. 



Mr. J. G. Jeffreys exhibited several specimens of the common whelk (Buccinum 

 undatum) having double opercula ; in one instance, a second or supplementary 

 operculum being piled on the usual one ; and in the others, there being two separate 

 opercula, instead of one. in each whelk. He adverted briefly to the different kinds 

 of monstrosity which occur in animals and plants, and said he believed this to be 

 the first case of a similar monstrosity in the Mollusca. He observed that the 

 monstrosity under consideration appeared to be congenital, and not to have arisen 

 from an accidental loss of the original organ, because in some of the specimens both 

 opercula were cases of hypertrophy, and in the others of atrophy ; and he mentioned 

 that all the specimens came from the same place ( Sandgate in Kent ), showing a 

 repetition, and perhaps an hereditary transmission, of the same abnormal pheno- 

 menon ; and he suggested that thus permanent varieties might in course of time 

 be formed, and constitute what some naturalists would call " distinct species." He 

 adduced in support of this view, the case of a reversed monstrosity of the common 

 garden snail (Jfclix aspersd), having been bred for many years in succession by the 

 late M. d'Orbignv in his garden at Rochelle, as well as many instances of a 

 reversed form of almond whelk {Fusus antiquus) having occurred in the same 

 localities on the coasts of England and Portugal, such being the normal form in 

 the crag;. 



"6" 



On the British Teredines, or Ship- Worms. 

 By J. G. Jkffkeys, F.R.S. 



After observing that his researches had not been confined to the British Tere- 

 dines, but that lie had recently had an opportunity of meeting all the French 

 naturalists who had published on the subject, as well as of studying all the access- 

 ible collections and books, lie treated the matter first in a zoological point of 

 view, and gave a short history of the genus Teredo, from the time of Aristotle and 

 his pupil Theophrastus to the present time ; especially noticing the elaborate mono- 

 graph of Sellius, in 1733, on the Hutch ship-worm ; the valuable paper of Sir 

 Everard Home and his pupil Sir Benjamin Brodie, iu 1806 ; and the physiological 

 essays of Quatrefages, in 1840. 



