416 



DACTYLIOSOLEN. 



R. alata Brightw. (Q.J.M.S., 1858, vi., p. 95, pi. 5, f. 8 ; h.v.h. 

 Atl., pi. 79, f. 8*), plate 33, fig. 887. 



Frustule cylindrical, narrow ; calyptra rather long, much flattened, obtuse, 

 without a mucro, with the line of articulation twisted spirally, showing a small 

 spine at its base. Scales rhombical, finely striate. 



Marine. North Sea (Schiitt), Kattegat (Cleve), Yarmouth (Kitton), East Coast of England 

 (Norman). 



R. Stolterfothii (H. P. Monog., p. 13, pi. 1, fig. 17-18; Encampia 

 striata Stolt.), a cylindrical arcuate form, is met with rather frequently in 

 pelagic gatherings and has been recorded by Stolterfoth from the surface of 

 the Dee, and has been raised by M. Schiilt to the rank of a genus under the 

 name of Henseniella, which the author defines in the following manner : 



Henseniella Schiitt, 1893. Frustule elongated, cylindrical, twisted, 

 recurved, forming spiral chains ; membrane slightly silicious, showing numerous 

 annuliform septa ; valves elliptic, plane, or concave. 



This genus includes two forms : Henstniella (Pyxilld) Baltica {Hens.) 

 Schiitt and Henseniella Stephanos (Hens.) Schiitt. 



GENUS 85 DACTYLIOSOLEN 

 CASTR., 1886. Per. em., 1892. 



Frustules cylindrical, annulate ; valves 

 plane, circular, symmetrical, without spines 

 or processes, sometimes showing a crown of 

 marginal dots. 



This genus was established by Count Castra- 

 cane for a single form, D. antarctiens represented 

 in the margin (fig. 134). Mr. Peragallo has 

 extended it somewhat so as to admit into it 

 different badly-classed forms, which link the true 

 Rhizosolenia to Melosira. 



No Dactyliosolen belongs to our regions. 



Dactyliosolen antarctiens. 



