REPORT ON THE DIATOMACE7E. 71 



Ehizosolenia inermis, d. sp. (Plate XXIV. figs. 7, 8, 10, and 13.) 



Annulis distinctis ; striis a?gre perspicuis ; processu calyptriformi terminali truncato 

 et lineola brevi loncitiulinalitcr sicnato. In mari Antarctico. 



The four cylindrical frustules here shown are composed of rings of trapezoidal plates, 

 and terminate in oblique calyptrae. It is noteworthy that in all the terminal mucrones 

 are alsent, and that the extremities of the calyptrae are truncated, each being ornamented 

 by a short longitudinal line, the whole reminding the observer of the shape of a pen. 

 This line seems to represent the mucro which is peculiar to other Rhizosolenian species, 

 a belief which is substantiated by the fact that in fig. 8 a trace of the line may be 

 perceived in the cavity, which is so disposed as to receive the extremity of the succeeding 

 frustule. It is therefore of the utmost importance to remark that in the definition of 

 the genus the terminal mucro, although a very general, cannot be regarded as an 

 essential characteristic. Although varietal differences may exist in the four frustules 

 figured they have all been, for the sake of convenience, grouped under one specific name, 

 which has been suggested by the common character of their extremities just alluded to. 



Rhizosolenia polydactyla, n. sp. (Plate XXIV. fig. 2.) 



Annulis brevioribus" crebris ; striis imperspicuis ; processu calyptriformi brevi et acuto 

 mucrone armato. In mari Antarctico. 



This frustule is peculiar on account of the shortness and multiplicity of its rings. The 

 terminal mucro is strong and very acute, even more so thau is indicated in the figure. 



The specific name of this Antarctic form is intended to be indicative of the remarkable 

 character of its rings. 



Bhizosolenia ingequalis, n. sp. (Plate XXIV. fig. 15.) 



Forma subcylindrica, constans annulis transversis parallelis ; processu calyptriformi 

 composito, in acutissimum mucronem exeunte. In mari Sinensi ad Hong-Kong. 



This Diatom was observed in a surface gathering which was made in the neighbour- 

 hood of Hong-Kong. It is remarkable on account of the inequality of its transverse 

 diameters at different parts, an anomaly which may be attributed to regional inequalities of 

 pressure on the rings, which, instead of being round, are oval in section. It is also 

 especially noteworthy that the calyptriform process does not consist merely of a single 

 piece, but is made up of two or three rings or distinct parts. 



Rhizosolenia sima, n. sp. (Plate XXIV. fig. 11.) 



Frustulis subcurvatis ; calyptra brevi in obtusum brevissimum mucronem desinente ; 

 imperspicue striata. In extremo mari Antarctico ad glacies impervios. 



A singularly strange aspect is presented by the present frustule, which cannot be 

 regarded as an accidental or monstrous form, as it has been frequently met with in the 



