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



when seen in the zonal aspect, are symmetrical in themselves, but each is unsymmetrical 

 with reference to the transverse axis. Their surface is ornamented with large irregularly 

 disposed granules. No distinct connecting zone is seen, the two adjoining valves being 

 immediately united. In some frustules a smooth belt may be observed between the 

 two valves. 



The specific name has reference to the form of the frustule. 



Eucampia balaustium, n. sp., var. minor, nov. (Plate XVIII. fig. 6.) 



We have here represented a form which must be regarded as a mere variety of the 

 preceding type, differing from it in its smaller size, and in having the extremities some- 

 what blunted. 



It is important to note that, as may be observed in this figure, the last valve in the 

 series differs from the others, having the two extremities less prominent and of equal length. 

 In this circumstance Eucampia resembles Bacteriastrum, Clisetoceros, and probably also 

 Hemiaulus. 



Molleria (Cleve), Cstr. 



As above referred to (see Eucampia, p. 97), this genus, instituted by Cleve in honour 

 of M. Moller, of Wedel, Holstein, does not differ essentially from Eucampia, except by 

 the presence of a nodule in the centre of the valve, and by possessing two unequal ter- 

 minal processes. Hence the genus may be defined as follows : — Frustula cuneata in 

 spiralem seriem conjuncta ; valvis ovalibus centrali nodulo instructis, et in duos inajquales 

 processus desinentibus ; zona connectens plerumque crebre costata vel plicata. 



Molleria cornuta, Cleve. (Plate XXV. fig. 8.) 



We have here shown a small specimen of Molleria cornuta, Cleve, 1 which has hitherto 

 been unique in its kind. Two frustules are seen in series, and the shorter of the two 

 has been checked in the act of fission, so that two new valves, in process of formation, 

 may be observed through the belt. Similar observations have already been made in the 

 case of Biddulphia, and in other types possessing two symmetrical valves. 



Molleria antarctica, n. sp. (Plate XVIII. fig. 8.) 



Forma cuneata grandiuscula, valvis ellipticis vix perspicue punctulatis et nodulo cen- 

 trali instructis ; cingulo costulato vel plicato, bipartito ; processibus terminalibus parum 

 productis. In mari Autarctico. 



1 Cleve, Examination of Diatoms found on the surface of the Sea of Java, Bihang k. Svensk, Vet. Akarf. 

 IlandL, Bd. I. No. 11, p. 7, Stockholm, 1873. 



