PARALLELODON GEINITZI. 109 



of the Geological Survey, Jermyn Street. This specimen is slightly faulted in front, 

 and the contour is therefore not the real one. Posteriorly the teeth on the hinge- 

 plate are shown to terminate at some distance from the posterior end. The pallial 

 line is very well marked in this example. 



PI. XII, fig. 5, shows the anterior part of the hinge-plate, with traces of several 

 oblique short teeth, and the broad ligamental area. 



PI. XII, fig. 2, has the test preserved, and shows the surface of the valve 

 perfectly. 



Phillips described his shell very briefly, as follows : — " Twice as wide as long, 

 gibbous, oval, front inflexed, surface undulated ; reticulated in the posterior slope 

 near the hinge." In the full-grown specimens the surface at the lower border 

 becomes much less smooth than above; and the cast referred to above, PI. VIII, 

 fig. 9, shows this characteristic detail. The species seems to be a very rare one, 

 Thorpe Cloud being the only locality where I have obtained it in any quantity. 



In casts there are two or three broad irregular concentric sulci, most apparent 

 over the median portion of the shell, PI. VIII, fig. 9. These are evidently 

 depicted in the original figure, which makes me think that it was drawn from a 

 cast. 



This species seems to have attained a very large size. Fig. 1, PI. XIV, from 

 the Gilbertson Collection of the Natural History Museum, measures 77 mm. antero- 

 posteriorly and 38 mm. in its dorso-ventral diameter. The only other species of 

 the genus which attains to anything like this size is P. ornatissimus, which differs, 

 however, from P. obtusvs in its ornament; further the posterior end is more 

 expanded, the posterior margin more oblique, and the posterior-inferior angle 

 much produced. The ligamental area is very broad and elongate. 



Parallelodon Geinitzi, de Koninch, 1885. Plate XI, figs. 17 — 21; Plate XIII, 



figs. 10, 10 a. 



Parallelodon Geinitzi, de Koninck, 1885. Ann. Musee E. Hist. Nat. Beige, 



vol. xi, p. 159, pi. xxiv, figs. 50, 51. 



Specific Characters. — Shell small, transversely oblong, subcylindrical, very 

 narrow in a dorso-ventral direction, but broader behind than in front. The anterior 

 end is small, compressed, and pointed above ; the border begins above at a right 

 angle with the hinge-line, and immediately curves downward and backward, 

 passing into the inferior border ; this is so very slightly convex downwards as to 

 be almost straight. The posterior border is straight, obliquely truncate from 



2.2 



