

CRUSTACEA. 161 



Siphuncle situated near the ventral side of the tube; its elements in the interseptal 

 spaces have not been observed. 



Test not preserved. Internal mould smooth." 



Remarks — The only specimen in the Missouri collections of Walker Museum is a 

 fairly perfect living chamber 68 mm. by 56 mm. at the detached end; 75 mm. long. 

 The center of the siphuncle is 7 mm. from the lower edge of the chamber. The aper- 

 ture is subtriangular with its greatest diameter about 43 mm. The outline of the 

 aperture is indistinct. 



Occurrence — Grand Tower limestone of Little Saline Creek. 



ARTHROPODA 



Class CRUSTACEA 

 Subclass Trilobita 

 Order Opisthoparia 



Family Proetidae 



Genus Proetus Steininger 



Proetus crassimarginatus Hall and Clarke 



Plate 39, figure 4 



PI. 21, figs. 8-10; pi. 30, figs. 6-8 



Description and synonomy on pages 125 and 126. 



Remarks — A few fragmentary pygidia of this species are in the collections. 

 Occurrence — Grand Tower limestone of Little Saline Creek. 



Proetus haldemani Hall 



Plate 39, figure 12. 



1861. Proetus Haldemani Hall, Descriptions New Species of Fossils, etc., p. 74. 

 1888. Proetus Haldemani Hall and Clarke, Pal. New York, Vll, pp. 113-116, pi. 21, 

 figs. 7-9; pi. 23, figs. 13-15. 



Description abbreviated from Hall — -"Outline sub-elliptical or elongate-ovate. Sur- 

 face convex, distinctly and equally trilobate. Length to width as 1.7. 



Cephalon semicircular or semi-lunate in outline; border broad, flat and rounded at 

 the edge; widest in front and narrowing toward the genal angles, where it is very faintly 

 produced. Surface evenly convex. 



Facial sutures normal, rapidly approximating on the frontal margin. • 



Glabella broadly conate, constricted opposite the anterior angles of the eyes. Sur- 

 face depressed-convex. Length and greatest width about equal; the anterior extremity 

 scarcely reaching the marginal sulcus, the posterior margin ending abruptly at the occi- 

 pital furrow. The anterior and lateral margins are bounded by shallow and inconspicuous 

 furrows. Lateral furrows, as shown upon the cast of the lower surface, in. four pairs, 

 accompanied by the posterior accessory depressions. Of these furrows the first pair is 

 very short and transverse, the other three pairs and the accessory pair inclined obliquely 

 backward. The fourth pair is strong and reaches to the posterior margin, but does not 

 open into the occipital furrow. Upon the surface of the test these lateral furrows would 

 undoubtedly be less conspicuous, but no specimen has been observed in which the 

 crust of the glabella is retained. Occipital lobes moderately strong; occipital furrow 

 6 



