40 THE VOYAGE OF H.M.S. CHALLENGER. 



Those species which, like Amphiprora alata, Ehrenb., Kg., are bent spirally, are the 

 most difficult to understand, being very frequently seen with a cone-shaped profile. Those 

 that are not spirally bent have the zonal side more or less panduriform owing to a central 

 constriction resulting from the bilobate form of the wings. The genus may, accordingly, 

 be conveniently divided into two sections, one comprising the non-spiral and the other the 

 spirally bent forms. 



Amphiprora plicata, Greg., var. japonica, nov. (Plate XXX. fig. 8.) 



A small specimen from the Sea of Japan is here represented. It greatly resembles 

 Amphiprora plicata, 1 Greg., having a panduriform profile owing to the existence of a deep 

 central constriction. In both, too, the extremities are rounded and the connecting zone 

 is marked by longitudinal lines or folds. In the species determined by Gregory, however, 

 no noteworthy marks occur at the lines of junction between the wings and the valves, 

 whereas in the frustule from the Sea of Japan more salient points occur at intervals of 

 about four strise. These puncta are probably formed by a thickening of the stria?, so that 

 a kind of longitudinal keel somewhat similar to that which is found in the genus Nitzschia 

 is the result. Although this characteristic is well marked it cannot be viewed as of specific 

 importance, so that the Japanese form must be looked upon as a variety of Gregory's species 

 belonging to the non-spiral section of the genus. 



Amphiprora fimbriata, n. sp. (Plate XVII. fig. 15.) 



Spiralis, oblongo-elliptica ; apicibus late rotundatis ; ala vel carina undulata ; striis 

 imperspicuis. In mari Pacifico. 



This very elegant oblongo-elliptical form belongs to the spiral section of the genus. The 

 wings, which have their origin in the subcordate inconspicuously striated valve, are also 

 bent spirally, and, as if to adapt themselves to the curvature of the frustule, they are 

 transversely undulated. This remarkable disposition of the alee has not hitherto been 

 recognised in any other species, and cannot but be regarded as of specific importance. The 

 apices are broadly rotundate. 



Achnanthes, Bory. 



Among the pedunculate Diatoms, Bory of St. Vincent established this genus in 1822. 

 It has been defined by Professor W. Smith 2 as follows: — "Frustules geniculate, united 

 into a filament which is stipitate or attached, valves striated, unsymmetrical, the lower with 

 a longitudinal and transverse line, and central and terminal nodules, the upper with a 

 longitudinal line only." 



1 Gregory, op. cit., p._33, pi. iv. fig. 57. 2 Op, cit., vol. ii. p. 25. 



