LAMELLIBRANCHIATA. | UPPER PALZOZOIC MOLLUSCA. 519 
plumes, separate Solenimya from even the most nearly allied forms, except Glycimeris, with which it has much 
similarity in the shell. 
Recent ; very few rare species in the Mediterranean and Australian seas; quoted doubtfully in the Upper 
Palzeozoic rocks, as the following species or varieties are inequiyalye. 
SoLeNIMYA? PRiIM@VA (Phill.) Pl. 3. F. fig. 3. 
Ref—Phill. Geol. York. Vol. II. t. 5. f. 6. 
Desc.—Elongate-oblong ; posterior end only one-fourth the length of the shell, narrowed by a long, 
wide, concave cartilage lunette from the beaks, obtusely rounded at the extremity; beaks small, very much 
compressed, not prominent, oblique towards the posterior end; dorsal margin very slightly convex; hinge- 
line nearly as long as the shell; anterior end slightly narrowed, subtruncate, rounded, gaping ; ventral margin 
nearly straight, slightly convex, or sometimes faintly concave a little behind the middle ; valves gently convex, 
deepest a little in front of the middle, becoming gradually compressed towards the ventral margin, and rather 
abruptly arched towards the anterior cardinal margin (resembling the posterior slope of many shells). Surface 
glossy, faintly radiated from the beak towards the long anterior end, by flat, not prominent, irregular ridges, 
averaging their width apart, and from one-third to half a line wide, usually flat in the middle with prominent 
edges, appearing like a pair of narrow striz ; rarely a third intermediate raised line: surface under the lens with 
extremely fine, radiating, slightly flexuous strice (sixteen in half a line), crossed by concentric, extremely minute 
plications or strize of growth, about equalling the microscopic longitudinal striation in size. Internal casts shew 
slight indications of the external radii; anterior muscular impression large, faintly marked, with a faint sulcus 
diverging from a little in front of the beaks towards its posterior superior extremity (only visible in some speci- 
mens) ; posterior muscular impression at the short end very strongly marked, with a thick oblique ridge, leaving 
a sulcus in the cast running from the beak along its anterior or inner margin; on its outer or posterior margin 
the slight thickening of the external cartilage support is clearly seen, and the reflected gaping edge of the lunette 
in some specimens, as well as the impression of the internal part of the cartilage within the apex of the beak ; 
immediately within the long anterior cardinal edge is the shallow sulcus of the slight thickening of the dorsal 
margin. Average length one inch eight lines, proportional length of posterior end measured along the 
slope =, width from beak to ventral margin ;;, ditto in middle of length ;%, width of anterior end *, depth 
of both valves =, (occasionally two inches three lines long). 
The agreement seems so perfect between this fossil and the recent Solenimya, except in being slightly 
inequivalye and the greater strength of the posterior muscular impressions, that I think with Prof. King that 
his genus Janeia is not required for it, at the same time that I do not think with him that Phillips’s observations 
tend to prove that the short end of the shell is the anterior; and I have used the terms anterior and posterior as 
they are used by other writers in describing Solenimya, and contrary to the way in which they are used in other 
shells. The pallial line meets the anterior edge of the posterior adductor at a very acute angle, forming a short 
angular sinus, directed almost angularly upwards towards the beak; not, I think, a siphonal sinus. In all our 
numerous specimens the left valve is larger at the beak than the right one, as has been remarked by M, de 
Verneuil. 
Position and Locality—Very common in the impure carboniferous limestone of Lowick, Northumberland. 
Explanation of Figures.—P1. 3. F. fig. 3, left valve, natural size ; internal cast, shewing the large muscular 
impressions, faint anterior oblique ridge from the beak, and (imperfectly) the casts of the ridges behind and 
before the posterior muscular impression ; fig. 3a, ditto, back view, shewing the cartilage supports behind the 
beaks, as well as the faint divergent ridges in front of them. 
[rasc. 111.] 3X 
