168 



viewed by transmitted light, this resemblance was most complete. 

 There were the same apparent siphons or lateral communications 

 passing from the chamber, and for a little time I felt disposed in 

 this instance to adopt his views. There were also, what he conceived 

 to be the " bands of aggregated large apertures near the septa of the 

 chambers (see his Plate 5, fig. a, d, Taylor's ' Scientific Memoirs,' 

 vol. iii.), and the " numerous small apertures over the entire surface of 

 the shell." No one dissimilar feature existed. 



After a more elaborate examination, however, I ultimately became 

 satisfied that the structure of these specimens was similar to that of 

 P. crispa. When viewed as a transparent object, the lateral tubes ap- 

 peared almost to project from the posterior or concave side of each 

 septum and to be prolonged far into the cavity of the antecedent 

 chamber. It became evident, however, that the visible line of the sep- 

 tum was merely that of the projecting central portion, which was very 

 much in advance of the lateral sutures, where the walls of one chamber 

 are attached to those of its antecedent ; but since in the latter part, 

 there are on each side two nearly horizontal and parallel layers, no 

 distinct shadow is found ; whilst in the projecting centre, where the 

 septum assumes a direction vertical to the stage of the microscope, the 

 light is intercepted, and a distinct outline rendered visible ; the tubes, 

 which, in this species are very much shorter than in P. crispa, appear- 

 ing of course posterior to this outline, and seeming to be chiefly in 

 and belonging to the cell behind it. 



Specimens, however, frequently occur in which fractures extend 

 across the first cell, reaching the true lateral junction with the second 

 chamber, and exposing, without injuring, the anterior wall of the latter. 

 These fractures traverse the dark line constituting the apparent septum, 

 and reach the posterior extremity of the longest of the tubes, showing 

 most distinctly that the latter terminate, as in P. crispa, with the pos- 

 terior boundary of the cell or chamber to which they belong. The 

 same species also satisfied me that what in M. Ehrenberg's specimens, 

 he considered to be bands of larger foramina ranged along the lines of 

 the sinuses, are in my forms, tubercular elevations on the exterior of 

 the calcareous shell, such as 1 have already mentioned as existing 

 in the corresponding portions of P. crispa (fig. 4,<7). 



Though I would speak with the greatest diffidence, not having seen 

 M. Ehrenberg's specimens, I cannot help suspecting that his Geopo- 

 nus stella-borealis is our widely-diffused little' Polystomella, — and 

 that the illustrious Prussian has, on this point, been inadvertently led 

 into some errors by his favourite plan of mounting his objects in 



