4+ 



MELOSIRA. 



ANALYSIS OF SPECIES. 



I. Valves simply punctate. MELOSIRA. 



* Junction surfaces of frustules convex. 



f Valves with only a slight keel. Frustules globular, 

 Valves with one usually in long bands . . . . M. nummuloides. 



or two projecting -{ 



keels. j Valves with two subcorneal keels. Frustules usually 



(_ solitary or united by two individuals . . . M. Westii. 



Frustules very robust, breadth usually greater than 

 length, subglobular or disciform, with valves not 

 constricted between the sutural zone and the apices 

 which are strongly convex . . . M. Borreri. 



Valves without a 

 keel. 



Frustules 



constricted 



between the 



sutural zone 



and the 



apices, which 



are more or 



less 



flattened. 



Frustule moderately robust, length 

 usually slightly greater than 

 breadth, apices much flattened . M. varians. 



Frustule slightly robust, length 

 usually greater than breadth, 

 apices very slightly flattened . M. Jurgensii. 



** Junction surfaces of frustules plane, often denticulate. 



i. FRUSTULE SHOWING A SULCUS NEAR THE SUTURAL MARGIN. 



Frustule robust, broad ; valve showing at the centre some coarse isolated 

 granules . . . . . . M. Roeseana. 



Frustule more or f Length of frustules usually not much greater than 



breadth. Valve with rather strong granules 



M. distans. 



less narrow, 

 delicate ; valve 



entirely covered j Length of frustules usually greater than breadth, 

 with granules. [_ Valve with very fine puncta . . . M. crenulata. 



2. FRUSTULE WITHOUT SULCUS ON EACH SIDE OF THE 

 CONNECTING ZONE. 



Frustules very robust, walls very thick, breadth greater than length, finely 



striate ; disc with costae . . . . M. arenaria. 



Filamem formed of elongated frustules, with coarse 



conspicuous granules . . . . M. granulata. 



Frustule 

 moderately ro- 

 bust ; disc i pji ament f ormec i f short frustules, with granules 

 absent or only very delicate and obscure ; frustule 



costas. 



^ often containing imperfect septa 



M. Dickiei. 



II. Valves punctate and areolate. Paralia. 



A single form ... . . . M. sulcata. 



I. Valves simply punctate : MELOSIRA. 

 * Junction surfaces of frustules convex. 



M. nummuloides (Bory) Agardh. (Syst. Alg., p. 8; H.V.H. 

 Atl., pi. 85, f. 1 and 2*; Type No. 457), plate 18, fig. 608. 



