STROPHALOSIA. 45 



Strophalosia Morrisiana, Schauroth. Ein neuer Beitrag zur Palseontologie des 



deutschen Zechsteingebirges, p. 221, 1856. 

 — cancrini, Howse. Annals and Mag. of Nat. Hist., vol. xix, 2d series, 



p. 49, 1857 (not Productus Cancrini, Verneuil and 

 Keyserling). 



Shell nearly circular, or slightly oval marginally when full grown : concavo-convex, 

 and in general about as wide as long, the greatest breadth being situated towards the 

 middle or anterior portion of the shell. The ventral or larger valve varies much in degree 

 of convexity. It is evenly convex and without sinus in well-shaped individuals, while in 

 others the greatest gibbosity is situated towards the beak. The margin of the valve is 

 likewise sometimes either slightly bent upwards, or suddenly downwards, while in other 

 specimens the convexity is very moderate. The beak is regularly shaped, evenly rounded 

 and incurved in the larger number of full-grown specimens from certain localities (fig. 35), 

 showing no indication whatever of having adhered by any portion of its surface (var. 

 Humbletonensis, King) ; but other examples less favorably placed or developed in the 

 same and in other localities, show that the shell adhered or was adpressed to a greater or 

 lesser extent (fig. 25) ; and this is particularly the case with distorted shells (figs. 28 — 30), 

 where the beak is truncated, and more or less irregular in shape and growth {Strop//,, 

 lamettosa, type, and var. Morrisiana, King). The hinge-line is much shorter than the 

 width of the shell ; the area in the larger valve is narrow, and sometimes hardly visible in 

 those shells which possess an evenly rounded and incurved beak. It is also in such cases 

 linear and scarcely perceptible in the opposite valve, but becomes larger and better 

 developed in both valves in those less-perfectly shaped individuals, in which the beak 

 adhered to some foreign body, or did not extend beyond the cardinal edge (figs. 25 and 31). 

 The external surface of the large valve is ornamented at variable intervals by long, 

 adpressed, tubular, creeping spines, directed outwardly and downwardly, and often 

 adpressed for a distance of eight or nine lines before rising from the surface of the valve 

 (figs. 34 and 36), so that, when perfect, some of the spines must have exceeded an inch 

 in length ; but those on the lateral portions of the beak and cardinal edge stand 

 erect from their origin, or are slightly directed backwards. The surface of the valve 

 is also more or less distinctly covered by a multitude of minute, radiating, raised striae, 

 which increase in number by intercalation and bifurcation (figs. 40, 41), and are sometimes 

 so closely packed, that towards the middle of a specimen measuring one inch in diameter, 

 from eighteen to twenty may at times be counted in the space occupied by a couple of 

 lines (fig. 40) : they are also more or less irregular in their respective widths, and at times, 

 by the uniting of two or three, form the base of a spine (fig. 41). 



The dorsal valve is, in general, moderately or very slightly concave, and almost flat, 

 in very young shells, with a slight convexity at the umbone. The external surface also 

 presents numerous radiating striae, with small indented impressions at various intervals 

 (fig. 35). In the generality of specimens no spines existed on this valve, but that some 



