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On Orbiculina Adunca (Fichtel and Moll) and its 

 Varieties. 



By a. Earland. 



(^Read June 17th, 1898.) 



A few months ago Mr. Karop very kindly placed me in com- 

 munication with Mr. D. Bryce Scott, a member of this Club 

 residing abroad, from whom I subsequently received a quantity of 

 dredged sand from a West Indian locality, of the exact particulars 

 of which I am at present in ignorance. The material proved 

 upon examination to be a very typical Coral Sand, presenting no 

 special feature in its fauna, but of great interest, owing to the 

 abundance of one species : viz. , Orhiculina adunca of Fichtel and 

 Moll. This foram occurs in great numbers, and I do not think I 

 should be far out in estimating that quite one-quarter of the 

 entire bulk of the material is made up of this species in a more or 

 less perfect condition. Orbiculina is notoriously subject to great 

 variation in shape and size ; indeed, since the species was first 

 described by Fichtel and Moll, in the year 1803, the numerous 

 varieties have been figured and described by various authors under 

 about fifteen synonyms. I have succeeded in obtaining a very 

 complete series of the varieties from Mr. Scott's material, and 

 with your permission I will now attempt to give you a short 

 account of the life history of this foram, so far as it can be 

 gathered from the study of the dead shells, and to illustrate by 

 means of rough diagrams the method in which these protean 

 shapes arise. 



The genus Orbiculina, which consists of a single species only, 

 the foram now under consideration, belongs to the Imperforate 

 Foraminifera, in which the shell is entirely destitute of foramina 

 or apertures in the shell wall for the emission of the pseudopodia. 

 It is now located in the sub-family Peneroplidinse of the family 

 Miliolidse, the members of which are characterised by shells of a 

 porcellanous whiteness when viewed by direct light, turning to a 



