CARBONIFEROUS AGE. 21 



Length of a large individual, 0.31 inch ; breadth, 0.36 Inch ; convexity, 0.23 inch. Length of a young shell, 

 P.27 inch; breadth, 0.23 inch; convexity, 0.15 inch. 



a b c 



d e 



Spirifer (_Martinia) plano-convexus. 

 a. Side view of medium sized specimen, b. Ventral view of same. c. Dorsal view of same. d. Dorsal view ot a 

 larger transverse specimen, showiug the area and foramen, e. Hinge and internal view of a separated ventral. 



This little shell seems to agree exactly with the species described by Dr. 

 Shumard under the name Spirifer plano-convexus, and by Mr. McChesney, as 8. 

 gemmula, excepting that none of the (twenty or thirty) specimens we have seen 

 show the faint mesial depression or sinus in the ventral or larger valve, mentioned 

 by these gentlemen. As some of them, however, show a very slight flattening of 

 the middle of this valve, it is probable other individuals may possess an obscure 

 narrow sinus. It is worthy of note that the descriptions given by these gentlemen 

 agree quite as well with the European S. Urei, and we are strongly inclined to the 

 opinion that the form described by them, as weU as that now before us, really belongs 

 to that well laiown species. StiU, as our specimens nearly all differ from all the 

 figures of that species we have seen, in having the smaller valve, especially in adult 

 examples, a little concave, and the ventral valve destitute of a mesial sinus, while 

 they attain a much larger size, we have concluded to place them provisionally under 

 Dr. Shumard's name plano-convexus} 



As the closely allied Spirifer (Martinia) umhonatus (= Orthis umibonata, Conr.), 

 for which the new generic name Amboccelia has been proposed, is described as having 

 a " fibro-punctate" structure, we examined the structure of the species under con- 

 sideration very carefully, by transmitted light under a high magnifying power, to see 

 if we could detect the presence of punctures ; but after repeated trials we failed to ob- 

 serve any traces of them, though we saw distinctly the usual fibro-prismatic structure. 



Locality and position. — Manhattan, on Kansas River ; Upper Mill Creek, and 

 at various other localities in Eastern Kansas. Coal Measures. (Type of descrip- 

 tion and figures, 996, a, h, c.) 



Family PRODUOTID^. 



Shell free or attached by the substance of the beak, concavo-convex ; 

 valves articulated by teeth and sockets, or retained in place by the action 

 of muscles only; hinge with or without a cardinal area; oral appendages 

 without calcified supports, and probably fleshy and spiral ; surface more 

 or less spinous ; substance fibro-punctate. 



Animal unknown. 



• Since this was in type we have received a letter from Dr. Shumard, to whom we had sent the cuts 

 of this species, in which he says he has no doubt of its identity with his S. plano-convexus. 



