REPORT ON THE EORAMINIFERA. 
525 
In 1854 Reuss introduced the generic term Triplctsia for the three-sided Nodosarince 
of the Cretaceous formations ; but subsequently, in 1860, having found quadrangular as 
well as triangular forms, this name w T as changed to Rhabdogonium. 
The question to be determined is whether d’Orbigny’s name or Reuss’ S: — Orthocerina 
or Rhabdogonium — should now he adopted. Of the generic group, as now understood, there 
can be no doubt that the species which first received a name was d’Orbigny’s Vaginulina 
tricarinata ; and it is equally certain that, of the two species for which the term 
Orthocerina was used, the earlier in point of date, that which was subsequently referred 
to by the author as the typical form, does not belong to the present genus ; and further 
that the recorded characters, if intended for the forms under consideration, which is by 
no means clear, are far from accurate. Add to this the fact that a number of almost 
identical generic names, Orthoeera, Orthoceras, Orthoceratium, and others, were in 
general use, and had been applied to almost every variety of cylindrical or moniliform 
Foraminifera before Orthocerina was proposed, and the desirability of accepting the later 
term becomes manifest. 
The genus Rhabdogonium differs from Nodosaria primarily in the angular contour 
of the test. The shell is straight or only slightly bent, usually triangular or quadrangular 
in section, the salient edges being sometimes carinate. The segments are convex and 
compactly fitted together, their angular margins are somewhat drawn down towards the 
primordial end of the test, and there is little or no external constriction at the sutures. 
The aperture is a simple circular orifice at the centre of the somewhat tapering or pro- 
duced end of the final segment, sometimes situated in a short neck. 
The genus is widely distributed, especially in the North Atlantic and the South 
Pacific ; in the former it is usually found at depths of more than 300 fathoms, in the 
latter almost invariably at less than 300 fathoms. It occurs sparingly in the South 
Atlantic, but, so far as has been observed, is entirely wanting in the North Pacific. 
Geologically speaking, the genus makes its first appearance in the Lias, and becomes 
tolerably abundant in the Cretaceous period ; it is met with also in various Tertiary 
deposits, but not as a prevailing type. 
Rhabdogonium tricarinatum, d’Orbigny, sp. (PI. LXVII. figs. 1-3). 
Vaginulina tricarinata, d’Orbigny, 1826, Ann. Sci. Nat., vol. vii. p. 258, No. 4, — Module, No. 4. 
Rhabdogonium pyramiclale, Karrer, 1861, Sitzungsb. d. k. Ak. Wiss. Wien, voi. xvi. p. 19, pi. i. 
fig. 34. 
D’Orbigny’s Modele, No. 4, though easily recognised, is not a satisfactory rendering 
of the characters of this species. In the model the oral end of the test is truncate and 
the aperture a simple perforation placed in one of the angles, at no great distance from 
the margin. Such specimens may sometimes occur, but far more commonly the test 
(ZOOL. CHALL. EXP. PART XXII. — 1884.) ^ 67 
