1910.] NATURAL SCIENCES OF PHILADELPHIA. 125 



Three lamellae: axial, superior and basal — 

 Length 10, diam. 3 . 4 mm. 



(Shells with strong ribs throughout.) 



One lamella : axial — 



Length 12, diam. 3.3 mm. (Type specimen, pi. XIII, fig. 3). 



Two lamellae : axial and superior — 



Length 11.7, diam. 3 . 4 mm. 

 " 11, " 3.4 " 



10.7, " 3.2 " 

 10, " 3.5 " 



" 9, " 3 " Specimen figured, pi. XIII, fig. 5. 



Station 2. — Similar specimens occurred at higher levels at Station 2. 

 A large proportion of these specimens are ribbed throughout. The 

 lamellae in 15 shells opened are as follows : 



10 shells have 1 lamella, the axial. 

 5 shells have 2 lamellae, axial and superior. 



Station 3.- — Shells were taken under stones on the sunny side of the 

 ridge, and another lot on the summit of the ridge. The majority of 

 the shells are ribbed throughout, but some have the penultimate 

 whorl nearly smooth. Most specimens are 10 to 11 mm. long. In 

 13 opened: 



