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THE VOYAGE OF H.M.S. CH ALLEN GEE . 
varieties with an obtuse or rounded margin, and subglobular forms. The former genus 
also furnishes isomorpbs of the elongate partially uncoiled species of Cristellaria, such as 
Cristellaria crepidula and Cristellaria obtusata ; and the question has arisen whether 
these should be retained amongst the typical Cassidulince, or transferred to the genus 
Ehreribergina described on a later page ; but, as in the case of Cristellaria, it has been 
found impossible to separate such forms from the strictly convolute varieties ; and the 
precedent established in that genus has therefore been followed. 
There is, however, one modification of the type which is non-spiral throughout, and 
which bears about the same relation to Cassidulina that Nodosaria bears to Cristellaria. 
Specimens of this nature are exceedingly rare ; and, pending the discovery of sufficient 
material for the full elucidation of their structure, they have been assigned provisionally 
to a new sub-genus Orthoplecta (6p0o<s, straight, and irXeKroq, plaited). 
The test of Cassidulina is invariably perforate. The walls are thin, calcareous, 
hyaline, smooth externally, and free from surface-ornament of any kind. 
The distribution of living Cassidulince is world-wide, almost irrespective of latitude or 
depth. In the fossil condition the genus is not very common ; it makes its appearance 
in the Eocene period, and is represented from time to time in beds of later geological age. 
Cassidulina laevigata, d’Orbigny (PI. LIV. figs. 1-3). 
Cassidulina laevigata, d’Orbigny, 1826, Ann. Sci. Nat., vol. vii. p. 282, pi. xv. figs. 4, 5; — Modele, 
No. 41. 
„ pulchella, Id. 1839, Foram. Amer. M&rid., p. 57, pi. viii. figs. 1-3. 
„ punctata, Reuss, 1849, Denkschr. d. k. Akad. Wiss. Wien, vol. i. p. 367, pi. xlviii. fig. 
4, a. 1). 
„ laevigata, Williamson, 1858, Rec. For. Gt. Br., p. 68, pi. vi. figs. 141, 142. 
„ sicula, Seguenza, 1862, Atti dell’ Accad. Gioenia, ser. 2, vol. xviii., p. 109, pi. L 
figs. 7, 7a. 
„ laevigata, Parker and Jones, 1865, Phil. Trans., vol. civ. p. 377, pi. xvii. fig. 
64, a.b.c. 
The test of the typical Cassidulina Icevigata is nearly circular in outline, biconvex or 
lenticular, and has a thin, often slightly carinate, peripheral edge. The segments are 
numerous, long, narrow, much curved, and scarcely at all inflated ; and the sutures are 
but little excavated on the exterior. In some specimens the shell-perforation is scarcely 
visible, in others the pores are numerous and conspicuous. The peripheral keel never 
amounts to a feature of any importance, as in Cristellaria and some other genera ; at best 
it is very narrow and ill-defined, and seldom completely encircles the test ; in rare 
examples (fig. 3) it is more or less serrate or jagged. None of the various “ species ” 
enumerated in the foregoing synonymy present characters differing in any material 
respect from the type, nor have they any claim to be considered as even varietally 
distinct. 
