CYTHERELLA. 47 



XXI. CYTHERELLA. Subgenus, Jones, 1848. Genus, Bosquet, 1852. 



The members of this genus are separable with difficulty as to their probable 

 specific identities (see 'Monogr. Carbonif. Entom.,' Part I, No. 2, Pal. Soc, 1884, 

 pp. 57 — 69). For the recognition of the British Tertiary forms we propose to 

 keep certain types in view, referring our specimens to one or the other of the 

 several groups. 



Group I. — Typified by Cttherella compeessa (Miinster), as figured by Egger, 

 ("Ostrak. Ortenburg," 'Neues Jahrb., &c.,' 1858, p. 404, pi. v, fig. 2), with its flat 

 parallel sides and more or less wedge-like ends (in edge- view). To this we have 

 relegated C. Londinensis, Jones (' Monogr. Tert. Entom.,' p. 55, pi. v, figs. 20 

 and 22), besides " C. compressa, var. 2," fig. 19, of the same plate. See also 

 ' Geol. Mag.,' 1887, p. 450, pi. xi, fig. 19. (British Museum.) 



Group II. — Cytherella Muensteri (Roemer). These carapaces have their 

 greatest convexity near the middle or towards the hinder part of the valves. 



One of our specimens from Bracklesham belongs to this group, but we know 

 of none exactly like it, in its symmetrical, broad, and oblong outline, with nearly 

 equally rounded ends, median convexity toward the ventral edge, and broadly 

 ovate edge-view. Plate II, figs. 3 a, h, c. We have called it C. Roemeri (' Geol, 

 Mag.,' 1887, p. 458). 



Another is near Roemer's original figure (' Neues Jahrbuch fiir Min., &c.,' 

 1838, p. 516, pi. vi, fig. 13) in shape, though not so strongly punctate (Plate II, 

 fig. 10). In the ' Monogr. Tert. Entom.,' p. 56, pi. v, fig. 13, is a smooth variety ; 

 but fig. 12 is even more strongly pitted than is Roemer's fig. 13, and was recog- 

 nised as var. rectipunotata in the ' Geol. Mag.,' 1870, p. 157. 



Some allied forms, smooth and having the convexity more definitely in the 

 hitider third of the valves, are remarkably ovate in outline, and lanceolate in edge- 

 view. These are regarded as belonging to a new species (Plate II, figs. 4 and 

 8 a, h) called C. Reussii, after the late eminent microzoist of Prague and Vienna 

 C Geol. Mag.,' 1887, p. 458). In the ' Monogr. Tert. Entom.,' p. 54, pi. v, figs. 21 

 and 23 are also smooth, and belong to this group ; but they are obovate in outline, 

 like Bornemann's C. fabacea (' Zeitschr. deutsch. geol. Ges.,' vol. vii, 1855, p. 355, 

 pi. XX, fig. 2), to which they must be referred, as in ' Geol. Mag.,' 1870, p. 157; 

 and 1887, p. 458, pi. xi, fig. 17. 



Another of our Tertiary Gytlierellse is ovate-oblong, lanceolate in edge-view, 

 with acute-ovate end-view. This also we believe to be new (PL I, figs. 24 a, b, c), 

 and have named it C. DixoNi (' Geol. Mag.,' 1887, p. 458), in memory of one of 

 the most enthusiastic workers on the geology and fossils of Bracklesham, whence 



