GASTROPODA. 155 



Test thick, especially in the umbonal region; marked by distinct subequidistant, 

 rounded radii, with slightly concave interspaces, in which are often finer, or obscurely 

 developed rays; the right valve is usually more closely and less strongly marked by 

 them than the left. The radii are crossed and crenulated by elevated, lamellose, con- 

 centric striae, which are more distant and conspicuous on the right valve. In the young 

 shells, the radii are conspicuous on the wing; they are a little more distant on the body 

 of the shell, and often obsolete along the line of the junction of the wing with the body, 

 especially in the right valve. In both valves, the radii become obscure or obsolete below 

 the centre, and the surface is marked by strong, irregular, concentric, lamellose undula- 

 tions. The radii often become more or less obsolete upon the wing, while remaining con- 

 spicuous on the body of the shell. 



Ligamental area extending the entire length of the hinge line, much wider in the 

 left valve; marked by coarse parallel, undulating, longitudinal grooves or striae. There 

 is a conspicuous oblique posterior lateral tooth, and two strong cardinal folds beneath 

 or just anterior to the beak. Anterior muscular impression situated in the rostral cavity ; 

 the pallial line continues thence in a curve somewhat parallel to the margins of the shell, 

 turning inward below the middle of the height and joining the large muscular im- 

 pression." 



Remarks — Remains of this species are rare and fragmentary. The characters of 

 the ligament and teeth are not discernible. Concentric striae do not appear excepting 

 as lines of growth near the outer margins. The largest specimen is more than 10 cm. 

 long by more than 9 cm. from the tip of the posterior wing to the extreme front. 



Occurrence — Sandstone member of the St. Laurent formation, Little Saline Creek. 



Order TELEODESMACEA 

 Superfamily Lucinacea 



Family Lucinidae 

 Genus Paracyclas Hall 



Paracycles elliptica Hall 



Plate 36, figure 1. 



Description and synonomy on page 115. 



Occurrence — This is a common form in the Grand Tower limestone of Little Saline 

 Greek, Ste. Genevieve County. 



Class GASTROPODA 



Subclass Streptoneura 



Order Aspidobranchia 



Suborder Docoglossa 



Family Bellerophontidae 



Genus Bellerophon Montfort 



One specimen of this genus is in the collection of Walker Museum, but it is too 

 imperfect for identification. 



