MELOSIRA. 443 



var. nivalis (W. Sm.), (Coscinodiscus minor W. Sm. nee Ruiz.; 

 H.V.H. Atl., pi. 86, f. 25-27* ; Type No. 462), plate 19, fig. 617. 



Valve with stronger and more approximate puncta. 



Marine. Scotland (Baxter Coll., No. 2699). 



M. crenulata Klltz. (Baa, p. 35, pi. 2, f. 8 ; M. orichalcea 

 IV. Sm. ; H.V.H. Atl., pi. 88, f. 3-5* ; in Types No. 401, 481, etc.), plate 19, 

 fig. 618. 



Valve with finely punctate disc, puncta scattered, margins showing 

 numerous well-marked denticulations. Frustule much longer than broad, 

 showing on the margin of the valves a slightly marked sulcus, striate, with 

 striae generally somewhat oblique, about 18 in 1 c.d.m., consisting of some- 

 what elongated puncta. Diameter, "67 to 2-0 c.d.m. 



Fresh water. Probably not rare. Found throughout our regions. 



forma tenuis (M. tenuis Kutz. ; H.V.H. Atl., pi. 88, f. 9 and 10*), 

 plate ig, fig. 619. 



Differs from the type-form by the greater length of the frustules 

 and smaller diameter, which does not exceed '5 c.d.m. 



Fresh water. Lake in Park at Antwerp (H.V.H., Type No. 190). 



forma Binderiana (M. Bindcriana Kutz. ; H.V.H. Atl., pi. 88, 

 f. 16*), plate 19, fig. 620. 



Frustules excessively elongated. Length equal to 5-8 times the 

 diameter. 



Fresh water. Rouge-cloitre (Delogne). 



All these forms are sometimes met with in the same gathering and even in 

 a single filament ; they are therefore only forms deserving of being ranked as 

 varieties (Kitton). 



2. FRUSTULE WITHOUT A SULCUS ON EACH SIDE OF THE 

 CONNECTING ZONE. 



M. arenaria Moore (in Raifs Ann., xii., pi. 9, f. 4 ; H.V.H. Atl., pi. 



90, f. 1, 2 and 3*; Type No. 468), plate 19, fig. 621 (left-hand figures). 



Valve with very thick walls ; disc furnished with costse, which add to the 

 breadth and height, from near the centre to the circumference, where they 

 simulate spines ; centre slightly depressed and covered with puncta ; costae 

 about 6 in i c.d.m., fitting perfectly with those of the adjoining disc. 

 Frustule broader than long, finely striate ; stria? punctate in quincunx (about 

 18 longitudinal rows in i c.d.m.). Valve with sutural margin furnished with 

 costae on its thickened portion, and of which the apices fit together and 

 simulate two rows of beads. (In fig. 1 of H.V.H. Atl., pi. 90, these rows of 



