DA. 



:m.) 



broad frill which p greatly beyond the free emit ,> () f the- vahe.- m 



it's of that ^enu-. A- usual. the original conception <>f /ViHiiV/-/ was altoget 

 too broad. ami as. through the iv-tle-< ellorts of collector-, the species began to 

 multiply, it became clear that they fell naturally into several group-, whose import- 

 ance in. \\ith time ami study till then 'ion became, at first desirable. 



then nece. ary. 



Still. 1'i-iiiiitiii retains a l.iru'e number of species, the greater part <>f which are 



v equally divided l>etween the Lower ami I'pper Silurian ro.-k- Two or three 



rather ilonhtfiil have been describe.! from primordial strata, hut at least five 



I'evonian -p.-.-ie< ha\e been discovered and a- many more in the I^>wer ' 

 bon; i fter which the genusseems to have become extinct. With a few except ion- 



all the-e -pecies were described in papei .lies, Jones and Holl, Krause, and 



Dlrieh. 



I'UIMITIA MI.SM TI-siMA, tt. >/). 

 11. 



: linn : hik'ht 0.1U nun. 



TJ- small, rather elongate-elliptical in outline, without distinct dorsal 

 angles, the end- rounded and nearly equal, the anterior slightly narrower than the 

 other; valves rather strongly convex; sulcus narrow, sharply defined, extending 

 nearly half across the valve; surface smooth. 



This i> the smalle-t I'riinltin known to me. It is evidently related to the British 

 \Venloch -pecies. I', hutnilis Jones and Holl, but is smaller, relatively more convex, 

 with the ends more rounded, and the sulcus narrower. It is not very closely related 

 to any of the known American -pecies. 



awt locality. Lower part f th" T .main, ami at Oxf 



mi- mine 



PKIMITIA i MIAMI, n. ,tp. 



I'l.MK M.lil. 1 Hi. M. 



I nun.: liitfht 0. H7 nun.: thi.'knev- 0. 1", mm. 



Valves small, compressed-convex, slightly obli(|iie. -ubovate, without di-tinct 

 dorsal angles; posterior end wider and more broadly rounded than the anterior; 

 ventral margin convex; edges thin, without border: <ulcus represented by a r;r 

 larjje. though not very deep depr> ut in the middle (if the dorsal 



slope; surface marked by small punet.i . arranged in curved lines radiating from the 

 sulcus; in certain lights each rov irs a- occupying the bottom of a narrow 



groove. 



