DE. W. B. CARPENTER ON ORBITOLITES TENUISSIMA. 
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pores (fig. II., 2). Both these peculiarities were noticed in my former Memoir 
(pp. 215, 221), but were treated as merely varietal modifications. I now find, however, 
that they accompany one another very constantly ; and that the type is so well 
differentiated by them as to be fully entitled to rank as a distinct species, which I 
designate 0. duplex* Notwithstanding the difference in the surface-aspect of its 
disks, and the doubling of their marginal pores, the sarcodic body of this species 
conforms in every essential particular to that of the preceding. For each of its 
concentric annuli consists of a single cord (fig. II., 4, c c'), that passes through a 
Fig. II .—Orbit elites duplex. 
continuous circular gallery in the median plane of the disk, and carries a double series 
of columnar sub-segments (ad, b b'), which occupy chamberlets (fig. II., 1) that extend 
in vertical series to the two surfaces of the disk. But each annular cord, instead of 
giving off (as in 0. marginalis) a single stolon-process to initiate a sub-segment of the 
succeeding annulus, gives off two such processes between each pair of its own 
sub-segments (fig. II., 4, d d, d'd '); and these have separate passages through the septal 
plane—one above and the other below the annular canal, as shown in fig. II., 2,— 
* This species, as intimated in my former Memoir, appears to be the type described by Prof. Ehrenbf.rg 
(Abhandl. der Konig. Akad. der Wissenscliaften zu Berlin, 1839) as a Bryozoon, under the designation 
Amphisorus Hemprichii. As his conception of the generic characters of this type was fundamentally 
erroneous, and as he gave no diagnosis of the single species he created, I have not thought it necessary 
to preserve his specific designation. 
