112 CRETACEOUS LAMELLIBRANCHIA. 
Measurements : 
(1) (2) (8) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14) (15) 
Antero-ventral margm 47 45 42 40 38 35 35 34 33 30 26 26 25 24 22mm. 
Hinge-margin . » 20) 22 2420-20) 20 16 20 18916 13s 12515) 15 2am 
Diameter from the 
middle of the carina 
(perpendicular) — to 
posterior margin . 16 19 19 18 18 17 14 17 15 13 12 11 18 — 10mm. 
Thickness . : Bly PAL Aiksy sy UG} TS) sy UG ls ass” 1} 11) kes}. 0) ald semen 
1, 3, 4, 5, 7, 8, 10, 14 from the Crackers, Atherfield. 
2 * Perna-bed, Atherfield. 
6, 9, 11, 12, 13, 15 from Blackdown. 
Affinities —The presence of an umbonal plate shows that this species should be 
referred to the Dreissensiide. In the few specimens showing the interior I have 
found no trace of the anterior myophore (for the byssal muscle) which distinguishes 
Congeria from Dreissensia'—but further specimens to confirm the absence of this 
structure are desirable. From the Upper Eocene of the Paris basin, associated 
with marine fossils, M. Cossmann” has already described two species of Dreissensia, 
and that author confirms my reference of this Cretaceous species to the 
Dreissenstidee. 
This species may be allied to Mytilus tornacensis, d’Archiac, from the Tourtia 
of Tournay, of which I have seen one specimen, sent me by M. Piret (see p. 91). 
That species, however, appears to differ from ours in having the carina at 
a greater distance from the antero-ventral border, also in the presence of more 
distinct and regular growth-lines with ridges or grooves at right angles to 
them, the ridges being best marked on the antero-ventral face of the shell. I do 
not know whether it possesses an umbonal plate or not. M. subfalcatus, VOrbigny, 
from the Cenomanian, appears to have the concentric ribs more distinct on the 
carina than is usual in M. lanceolatus, but since this feature is seen in some 
specimens of the latter, and is generally present on the earlier parts of the shell, it 
can hardly be regarded as distinctive. 
D’Orbieny considered that his Mytilus Galliennei,®? which in outline is similar to 
the larger examples of M. lanceolatus, was identical with M. tornacens/s, @ Arch. 
The forms from the Aachen Greensand described by Miler as MM. tegulatus, 
Mill., M. lanceolatus, Sow., and M. falcatus, @’Orb., whilst referred by Holzapfel * 
! P. Oppenheim, ‘ Zeitschr. d. deutsch. geol. Gesellsch.,’ vol. li (1891), p. 923, pl. hi. 
> © Cat. Il. Coq. Foss. Hoc. de Paris,’ fascic. 2 (1887), p. 151. 
8 «Pal. Frane. Terr. Crét.,’ vol. iii (1844), p. 278, pl. ccexxxix, figs. 1, 2; ‘ Prodr. de Pal.,’ vol. ii 
(1850), p. 165. 
+ “Die Mollusk, Aachen. Kreide” (‘Paleontographica,’ vol. xxxv, 1889), p. 218, pl. xxv, figs. 
1—9. It should be noted that these figures are enlarged twice. 
