DR. W. B. CARPENTER ON ORBITOLITES TENUISSIMA. 



561 



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 O. 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 annul i consists of a single cord (fig. II., 4, c c'), that passes through a 



Fig. ll.Orlitolites duplex. 



continuous circular gallery in the median plane of the disk, and carries a double series 

 of columnar sub-segments (a a, 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. EHRENBERG 

 (Abliandl. der Konig. Akad. der Wissenschaften zu Berlin, 1839) as a BRYOZOON, under the designation 

 AmpMsorus 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. 





