874 CAKBONIFKROUS FORMATIONS AND FAUNAS OK COLORADO. 



1887. rroditflii.i iiiiiricaliis. Ilfrrick, Sci. Lab. Denison Univ., ]'>iill., vul. 2, p. 49. 

 Coal Measures: Flint Ridge, Ohio. 



1888. Produdas maricalus. Keyes, Acad. Nat. Sci, I'liiUuleliiliia, I'roc.., \>. 228. 

 Lower Coal Measures: Des Moines, Iowa. 



1900. Produclus longispinu-i. Knight, Univ. Wyoming, Wyoming Kxp. Sta., Bull. No. 45, pi. 8, fig. 10. 



The form which, in Colorado, 1 have identified with Marginifei'a 'iimrioata, iiiaj' 

 be described a.s follows: 



Shell rather small, semicircular. Ears small, quadrate, and not prolonged. 

 Hinge line about equal to the greatest width. Curvature moderate, not so great as 

 in M. .y)lendens. Surface marked by concentric nodo.se. wrinkles, strongest on the 

 ears, and by coarse, somewhat nodose striai, which number about 25 on a medium- 

 sized shell. It is entirely covered at short intervals by small spines spi'inging from 

 the ribs. The transverse diameter is usually from 16 to 19 mm. 



The dorsal valve is semicircular in shape with quadrate ears. The latter are 

 upturned, when looking at the interior of the valve, and defined by two ascending 

 and diverging ridges. The shell is nearly flat over the visceral poi'tion, but a 

 geniculation occurs about 10 mm. from the beak. 



The shells agree closely with what I consider typical Jf. muricata from the 

 Mississippi Valley, but with this exception, that while specimens of the latter are 

 (so far as mj' experience goes) nearly uniform as regards the size of the stria-, those 

 from Colorado vaiy from a degree of fineness comparable with the latter to consid- 

 erably coarser. The Colorado form is also somewhat more strongly arched. I have 

 considered the advisabilit}^ of distinguishing these coarse occidental shells bj^ a varietal 

 name, but as the}^ occur in immediate association with the typical form into which 

 the}' merge by insensible gradations, it seemed sufficient merely to call attention to 

 the circumstance in an informal manner. 



In addition to variation in the matter of striation, which has already been 

 referred to as occurring among these shells, variation, often of local occurrence and 

 appearing in most of the specimens from a station, has been noticed in size, abund- 

 ance of spines, and other matters. 



It is possible that imperfectly preserved material may have given rise to misap- 

 prehension as to the degree of variation in some particulars, as, for example, the 

 abundance of sj^ines, but, on the other hand, it may be that with more perfect 

 material I would have felt justified in discriminating subdivisions among the fossils 

 here assembled into a single group. 



Schuchert" retains Norwood and Pratten's name for this species, because Productus 

 tnuricatus Phillips, which has priority, is regarded by many as a synonym for JP. 

 costatus Sowerb3^ This course violates the rule, once a synonym always a synonym, 

 and can scarcely be allowed, but Norwood and Pratten's name will still hold if 

 Waagen's genus Marginifera, of which it is a representative, be accorded generic 



" V. S. Genl. Surv., Bull. No. 87, 1,S97. p, 327 ( P. mnricatiis). . 



