REPORT OX THE DIATOMACK.K. 75 



Loth of which many scale-like parts go to form the circumference of the tubes. These 

 parts are in both somewhat irregularly quadrate in outline, but they are relatively much 

 broader in fig. 11 than in fig. 14. As in the case of Rhizosolenia arafurensis only frag- 

 ments have been observed. 



Dactyliosolen, n. gen. 



In a tow-net, which was wrought on the surface of the Antarctic Ocean on 

 March 3, 1874, lat. 53° 55' S., long. 108° 35' E., some interesting forms, akin to the 

 Rhizosolenia;, Ehrenb., were collected. In both the form of the frustules is cylindrical, 

 aud in both it is composed of plates of trapezoidal outline — the Dactyliosolen cylinder 

 (Plate IX. fig. 7) being manifestly the result of the union of a series of hoops, which, 

 if detached along the lines of suture and spread out on a plane, would present long 

 linear profiles terminated by oblique parallel lines. But, on the other hand, in Dacty- 

 liosolen there is no trace of the calyptriform extremities, which are essential to the 

 Rhizosolenia?, so that it cannot be ascribed to the latter genus. Apart, however, 

 from this circumstance, it is of importance to observe that at intervals in the course of 

 the filament hyaline belts occur. Each of these seems to be a terminal belt of union 

 between the various frustules, any adjoining pair being separated by a space equal to 

 about one-tenth of the diameter of the frustule. It is also to be remarked that at the 

 lines of junction a few incipient granules or denticules may be perceived, and it is very 

 important that the cellules, which ornament the component rings of two adjoining 

 frustules, stand on the opposite and not on the corresponding margins of the rings. 



That the combination of such characters is sufficient to warrant the estabbshment 

 of a new genus must be admitted, and it has been named Dactyliosolen 1 from the 

 circumstance that the perfect tube is composed of a series of rings or hoops. 



Dactyliosolen antarcticus, n. sp. (Plate IX. fig. 7.) 



Forma cylindrica ; frustulum compositum ex pluribus annulis cellulatis ; cellulis 

 linearibus oblongis. In mari Antarctico.' 



This is the only species of the present genus that has yet been observed, and its 

 characters are consequently those of the genus. 



Chaetoceros, Ehrenb. 



The following is the definition of this genus given by Ehrenberg (vide Pritchard's 

 History of the Infusoria, p. 861): — "Frustules without striae, united with the adjacent 

 ones by the interlacing on each side of awns proceeding from the frustule, or from a 

 cingulum between the frustules, and so forming a filament." 



A more exact and at the same time more concise definition is found in Lauder's 



1 day.TuXiog, a ring; tfwX^u, a channel or pipe. 



