180 PROCEEDINGS OF THE ACADEMY OF [1890. 



Platyceras subrectum Hall. (Geol. Iowa, vol. I, pt. ii, Suppl., p. 

 89, 1859.) Preoccupied by Hall for an Upper Helderberg form. 

 Synonym of C. infimdlbulum (Meek & Worthen). 



Platyceras tortum Meek. (Proc. Acad. Nat. Sci., Phila., 1871, p. 

 171.) This species does not belong to Capulus. The general form, 

 the flattened character of the upper half of the body whorl, the 

 obtuse angularity toward the sutural line and the sei'ies of distinct 

 parallel costpe running transversely over the volutions, as w'ell ex- 

 hibited in the type specimens, all indicate that the species is actually 

 a partially uncoiled Naticopsis, probably not far removed from N. 

 ventricosa N. & P. A similar tendency in the whorls to become 

 separated is admirably shown in Naticopsis gigantea H. & W. from 

 the Devonic ; and also in Platystoma niagarense Hall from the upper 

 Siluric. The shell of Naticopsis torta (Meek) is extremely thin and 

 fragile, while the lines of growth are regularly and evenly curved, 

 both of which characters are seldom exhibited in the ancient Capuli. 



Capulus triplicatus Swallow. (Trans. St. Louis Academy Sci., 

 vol. I, p. 205, 1858.) Too imperfect for description. Apparently 

 does not even belong to the Gasteroj^oda. Probably a valve of a 

 Myalina ! 



Platyceras uncum Meek & Worthen. (Pi-oc. Acad. Nat. Sci., 

 Phila., 1866, p. 264.) Synonym of Capulus acutirostris Hall. 



Of the five following species nothing is known except the original 

 descriptions which are very meager and are unaccompanied by fig- 

 ures. They are apparently identical with species already described ; 

 but inasmuch as authentic specimens have not been examined their 

 synonymy will not here be considered. They are : Platyceras hert- 

 zeri Winchell, Platijceras vomerium Winchell, P. quincuxense Mc- 

 Chesney, P. hickmansense McChesney and Acroculia trigonalis Ste- 

 vens. 



Explanation of Plate II. 



Fig. 1. Capulus par alius (W. & W.) la. Lateral view of type 

 specimen [Museum of University of Michigan], lb. A 

 younger individual. 



Fig. 2. Capulus cyriolites (McC.) Lateral aspect. 



Fig. 3. Capulus obliquus (Keyes). Lateral view of type. 



Fig. 4. Capulus tribulosus (White). 4a. A rather small shell, 

 from above. 4b. Same from side. 



