CRUSTACEA. 125 



Family Phragmoceratidae 



Genus Gomphoceras Sowerby 



Gomphoceras sp. undet. 



Plate 29, figure 7 



Only one specimen of Gomphoceras from the Missouri Devonian was collected by 

 the writer and his assistants. It came from the Mineola of Ralls County. It resembles 

 closely Gomphoceras solidum Hall from the Goniatite limestone of New York. Both 

 ends of the specimen are missing. The sides of the part preserved diverge at an angle of 

 about 20 degrees. The air chambers are five millimeters deep. The living chamber 

 is so badly broken that little can be made out concerning it. 



ARTHROPODA 



Class CRUSTACEA 



Subclass Trilobita 



Order Opisthoparia 



Family Proetidae 

 Genus Proetus Steininger 

 Proetus crassimarginatus Hall and Clarke 

 Plate 21, figures 8, 9, 10; plate 30, figures 6, 7, 8 



1888. Proetus crassimarginatus Hall and Clarke, Pal. New York, vol. VII, p. 99, 



pi. 20, figs. 6-8, 20-31; pi. 22, figs. 20-26; pi. IS, fig. 8. 

 1901. Proetus crassimarginatus. Kindle, 25th, Ann. Rept., Indiana Dept. Geol. Nat. Res., 



p. 750, pi. 30, figs. 1, la, 2, 5, 6. 

 1910. Proetus crassimarginatus Grabau and Shimer, North American Index Fossils, 

 II, p. 300, fig. 1611. 



Kindle 's description — "Glabella large, subquadrate; surface convex, slightly 

 flattened on top, marginal furrows shallow; three to four pairs of lateral furrows, directed 

 obliquely backward; these are developed on the lower surface of the glabella and reveal 

 themselves in specimens which are not exfoliated only by their darker color showing 

 through the semitransparent crust. Occipital lobes are relatively small but well de- 

 fined; occipital furrow narrow and shallow. The border of the cephalon is usually 

 narrow and much thickened in front. 



Thorax composed of ten segments ; axis broad and strongly arched ; pleurae flattened 

 for half their width, then sloping abruptly to the margin; the segments are flattened 

 and grooved upon the pleura. 



Pygidium semiovate, convex, sloping regularly to the lateral and posterior margin; 

 axis strongly arched both transversely and longitudinally, tapering to an obtuse ter- 

 mination. The anterior end is marked by from four to ten annulationS, the posterior 

 lateral area being smooth. In exfoliated pygidiae a larger number of indistinct annula- 

 tions may be counted. In crossing the summit of the axis the annulations arch back- 

 ward slightly." 



Remarks — Fragments of one species of trilobite are common in the highly crinoidal 

 phase of the Mineola near Montgomery City. Most of the remains are of pygidia. 

 Only two parts of cephala are in our collections. All of the specimens are small. The 

 largest pygidium is 16 mm. wide and 12 mm. long. Another is 7 mm. wide and 6 mm. 



