SEPTIFER. 109 
Modiola quadrata, Sowerby, from the Upper Chalk, is, I believe, only a 
somewhat crushed example of this species, similar to the one figured on our 
Pi VLE. tio. 12: 
Holzapfel considers that the forms from the Aachen Greensand, originally 
described by Miiller as Mytilus lineatus and M. sealavis, should be referred to M. 
lineatus, Sowerby. The Aachen species is very variable, and [ am greatly indebted 
to Prof. Holzapfel for the loan of six specimens which vary in their greatest length 
from 95 to 15 mm.' The Aachen shell is clearly distinct from our species ; it is 
more curved, more irregular, smaller, and with the radial ribs more strongly 
marked and not crossed by concentric ribs, so that the cancellate appearance is not 
seen. 
The form figured as Mytilus ciplyanus by de Ryckholt,? from Ciply and 
Maestricht, is perhaps a small example of S. lineatus (Sow.). 
M. xquatoralis, Mayer-Eymar,® from Somaliland, is perhaps an allied form, but 
is imperfectly known at present. 
Remarks.—The variations in this species consist chiefly in the amount of 
inflation and curvature of the valves, and in the flattening of the antero-ventral 
surface. 
The examples from the Hythe Beds are usually larger, rather more inflated, 
and have the antero-ventral surface more flattened than those found in the Upper 
Greensand and Cenomanian. But all the different forms which the shell takes may 
be seen at all horizons, and from the examination of a large series of specimens | 
am convinced that the Lower Cretaceous forms cannot be separated from those of 
the Upper Cretaceous. The relative proportions of the valves of course change as 
age increases. 
On account of the thinness of the shell the form of the valves has often become 
somewhat altered by pressure, and the shell itself—especially in specimens from the 
Hythe Beds—has often partly disappeared. 
None of the specimens I have seen show the interior of the valves, but some 
of the internal casts give indications of the presence of an umbonal plate. 
The name M. Cottx, Romer, is adopted by Geinitz (1873) for this species, and 
M. Cuvieri, Mathéron, by Pictet and Campiche (1867), since the name Mytilus 
lineatus had been used by Gmelin in 1789 for another form, and Modiola angusta 
was also preoccupied by Deshayes (1824). D’Orbigny in 1850 substituted the 
name sublineatus for lineatus, Sow. If Sowerby’s species be referred to Septifer, 
then his specific name may be retained. 
' It should be noticed that Holzapfel’s figures of this species are enlarged three times. 
2 “Mélanges Paldont.,” pt. 1 (¢ Mém. cour. et Mém. des Say. étrangers,’ vol. xxiv, 1852), p. 152, 
pl. ix, figs. 12, 13. 
3 *Vierteljahrs. nat. Gesellsch. Zitrich,’ vol. xxxviii (1893), p. 254, pl. i, figs. 7, 8. 
