REPORT ON THE EORAMINIEERA. 
657 
the peripheral outline being either irregular and subangular, as in figs. 1, 2, or almost 
circular, as in fig. 3. The segments are inflated and slightly embracing on the free side 
of the test, but their form and mode of combination are generally more distinctly 
seen on the superior or attached face. Average specimens have a diameter of about 
^-th inch (1 mm.). 
Under the name Planorbulina retinaculata, Parker and Jones have described a 
curious modification of the present species, “ which, besides being scabrous with granula- 
tion [like Planorbulina Iwrvatd], develops a large number of peripheral, subsidiary, 
tubular apertures, 'connecting together, and still keeping apart, the sarcode-chambers, and 
forming a kind of irregular network over the surface of the shells on which it grows ” 
(Phd. Trans, vol. civ. p. 380, pi. xix. fig. 2). 
Planorbulina mediterranensis is found in almost every sea within the temperate 
and tropical zones. It is commonest at depths of less than 50 fathoms ; but it occurs 
sparingly in the North Atlantic at 430, GOO, and 635 fathoms, and a single specimen has 
been obtained from a sounding taken north of the Canaries, at 1125 fathoms. In the 
South Atlantic it extends to a depth of 350 fathoms, and in the South Pacific as 
far as 255 fathoms. 
As a fossil the species has been observed in the Miocene of the Vienna Basin 
(d’Orbigny), in the later Tertiaries of Italy and Sicily (Jones and Parker, Seguenza) ; in 
the Crag of the east of England (Jones, Parker, and Brady), in the Post-tertiary 
formations of Norway (Sars, Crosskey, and Robertson), of Scotland (Robertson), of 
Ireland (Wright), and of the Island of Ischia (Vanden Broeck) ; and in the Fen-clays of 
Lincolnshire and Cambridgeshire (Parker and Jones). 
Planorbulina acervalis, n. sp. (PI. XCII. fig. 4). 
Test normally adherent, discoidal ; superior (attached) face flat, inferior more or less 
convex ; margin lobulatecl, with interspaces between the segments of the final whorl. 
General structure resembling that of Planorbulina mediterranensis, with the addition of 
a mass of minute acervuline segments covering to a greater or less thickness the free 
surface of the test. Diameter, -^th inch (1 mm. or more). 
The acervuline varieties of Planorbidina are distinguished from corresponding 
modifications of Tinoporus ( Gypsina ) by the retention of the normal Planorbuline 
arrangement of the segments on the attached face of the shell, and more especially by the 
peripheral apertures. 
Such forms are not uncommon amongst the islands of the Pacific, as well as in the 
Indian Ocean, and in the Red Sea. They frequent shallow water, and are most plentiful 
on bottoms of less than 20 or 30 fathoms, but are sometimes found at much greater 
depths. 
