168 Mr. H.J. Carter on the Form and Structure 



of the Nummulite, another " series of perforations of considerable 

 size, which pass directly downwards from the exterior, through 

 the superposed investing layers of the successive whorls, however 

 numerous, until they reach the floor and chambers of the central 

 plane, which they do not penetrate." These, he feels satisfied, 

 "always terminate over the septa, and actually pass into the 

 interseptal spaces." 



Now let us see how far these statements are confirmed by the 

 structure of the shells of Operculina Arabica, which were ob- 

 tained in the following way : — 



While medical officer on the survey of the south-east coast of 

 Arabia, I observed that Foraminifera were frequently brought up 

 <m the grease of the ship's sounding-lead, and after this I obtained 

 the loan of a lead which I used to cast for this particular pur- 

 pose myself. They were found to be most numerous in about 

 10 to 20 fathoms of water, rather in sandy than in muddy bot- 

 toms, scanty in deep water, and never (by the lead) among rocks 

 and coral-ground. In one bed passed over, which was several 

 miles in diameter, in about 20 fathoms of water, and about six 

 miles ofi" shore, the grease of the sounding-lead came up covered 

 with them at each throw; they were the largest living specimens 

 I have ever seen, and principally consisted of the genus Oper- 

 culina (D'Orbig.), Discorbis (Lam.). Most measured from 2 to 

 3-12ths of an inch in horizontal diameter, and one or two 

 3-lOths. Some contained animals, and others were empty ; the 

 latter were readily distinguished from the former by their pearly 

 whiteness ; while those which contained animals were invariably 

 covered with a thin greenish cuticle like the deciduous epidermis 

 of shells generally. 



The following is a description of this Operculina, which, as it 

 is most probably a new species, I have designated by the specific 

 name of " Arabica." 



Operculina Arabica (H. J. C). 



Description. Free, equilateral, oval or discoidal, thin, flat or 

 wavy; formed of one spire increasing gradually, not em- 

 bracing ; regular, equally apparent on both sides ; consisting 

 of 3-4 whorls, contiguous, enlarged on the outer border. 

 Chambers numerous, 1-75, narrow, apparent on both sides, 

 increasing gradually in length and breadth from a semitrans- 

 parent, prominent, central cell; radiating, reflected in their 

 outer third to a point, particularly in the last-formed whorl ; 

 divided by semitransparent septa, and covered externally 

 with a green substance like the epidermis of shells generally. 



