196 NEW YORK STATE MUSEUM 



between every two of which there are from three to five much finer apparently frorii twelve 

 to sixteen in the width of two lines. This may constitute a distinct species, but the. speci- 

 mens as yet collected are not sufficiently perfect to decide that point. 



Such specimens are evidently those we have now in hand. These 

 Strophonellas are well characterized, quite distinctly different from S. 

 punctulifera and among themselves express considerable diversity of 

 aspect. We may note first the characteristics of the prevailing expression 

 and then its differentials. It may here be observed that in these forms 

 again is manifested the prolixity of expression which accompanies and 

 indicates fecundity under favorable environment. 



Shell rather strongly concavo-convex, the normal convexity of the 

 ventral valve being continued for about one third the length of the shell. 

 The reversal is gradual but becomes abrupt specially in final stages. 

 The hinge line is straight and the cardinal angles very slightly extended, 

 subangular or even rounded ; cardinal area narrow, not striated vertically, 

 denticulate but slightly and only near the delthyrium of the ventral valve. 

 The opposite valve receives this denticulate edge in a narrow crenulated 

 groove. The muscle scar of the ventral valve is short and broadly flabellate 

 with somewhat thickened and elevated margins. The deltidium is usually 

 but partially developed. In the brachial valve the cardinal process is 

 strongly bifid, the separate parts being widely separated ; dental sockets 

 shallow. 



The surface of the valves is marked in the umbonal region by 16-20 

 sharp angular plications, simple throughout the normal contour of the 

 valves. These primary plications with those of the secondary series eventu- 

 ally constitute over the body of the shell a series of fine threadlike lines 

 separated by flat spaces in which lie fascicles of lesser order, sometimes but 

 a single series consisting of 6 or more lines, sometimes 3 or more subordi- 

 nate series. The general expression of the surface ornament however is 

 that of fine sharply fasciculate striation. On the interior of the valves the 

 surface is highly pustulose throughout except on the muscle areas, the 

 pustules being arranged in radial rows. 



These are the usual characters of the adult shell. The young of the 

 species are readily recognized as normally convex shells with sharp and 

 strong plications and this is a condition which when maintained to maturity 

 is expressed in such species as Strop heodonta arata of the 

 Schoharie grit of New York. 



Variant (i) equiplicata [pi. 40, fig. 12, 13]. We find a few 

 of these forms' in which the simple sharp plication of growth is not broken 

 up into fascicles but continues sharp over the body of the shell with very 

 sparse intercalations, so that the surface conveys the expression of subequal 

 plication and not of fasciculation. Such forms are at once distinguished by 

 their exterior. The initial striae are a few more in number than in the nor- 



