Mr. J. G. Jeffreys on British Foraminifera. 209 



The regular type of structure just described is subject to nume- 

 rous variations, into a minute description of which the author next 

 enters ; the general results being, that neither the shape nor dimen- 

 sions of the entire disk, the size of the nucleus or of the cells form- 

 ing the concentric zones, the surface-markings indicating the shape 

 of the superficial cells, nor the early mode of growth (which, though 

 typically cyclical, sometimes approximates to a spiral), can serve as 

 distinctive characters of species ; since, whilst they are all found to 

 present most remarkable differences, these differences, being strictly 

 gradational, can only be considered as distinguishing individuals. 

 It thus follows that a very wide range of variation exists in this 

 type ; so that numerous forms which would be unhesitatingly 

 accounted specifically different, if only the most divergent examples 

 were brought into comparison, are found, by the discovery of those 

 intermediate links which a large collection can alone supply, to be- 

 long to one and the same specific type. 



After noticing some curious monstrosities, resulting from an un- 

 usual outgrowth of the central nucleus, the author proceeds to in- 

 quire into the essential character of the Orbitolite, and its relations 

 to other types of structure. He places it among the very lowest 

 forms of Foraminifera ; and considers that it approximates closely 

 to sponges, some of which have skeletons not very unlike the cal- 

 careous net-work which intervenes between its fleshy segments. Of 

 the species which the genus has been reputed to include, he states 

 that a large proportion really belong to the genus Orbitoides, whilst 

 others are but varieties of the ordinary type. This last is the light 

 in which he would regard the Orbitolites complanata of the Paris 

 basin ; which differs from the fully- developed Orbitolite of the 

 Australian coast in some very peculiar features (marking a less com- 

 plete evolution), which are occasionally met with among recent 

 forms, and which are sometimes distinctly transitional towards the 

 perfect type. 



The author concludes by calling attention to some general prin- 

 ciples, which arise out of the present inquiry, but which are appli- 

 cable to all departments of Natural History, regarding the kind and 

 extent of comparison on which alone specific distinctions can be 

 securely based. 



June 2 1 . — The Lord Wrottesley, President, in the Chair. 



" Notes on British Foraminifera." By J. Gwyn Jeffreys, Esq., 

 F.R.S. 



Having, during a great many years, directed my attention to the 

 recent Foraminifera which inhabit our own shores, I venture to offer 

 a few observations on this curious group, as Dr. Carpenter, who has 

 favoured the Society with an interesting and valuable memoir on 

 the subject, seems not to have had many opportunities of studying 

 the animals in the recent state. 



Rather more than twenty years ago I communicated to the Lin- 

 nsean Society a paper on the subject, containing a diagnosis and 

 figures of all the species. This paper was r^adapd ordered to be 



