1912.] 



NATURAL SCIENCES OF PHILADELPHIA. 



541 



2 and 3, the margin of the embryonic shell and its connection with 

 that of the permanent patelloid shell is in the plane of the lower 

 edge of the lateral pouches or folds of Morse. The first of the 

 growth lines of the patelloid shell run under the protoconch below 



Fig. 2. — Protoconch of Acmoea 

 sp. from side, showing first of 

 adult shell. Line of base of 

 protoconch indicated by ar- 



rnws. 



Fig. 1. — Acmoea sp. Protoconch 

 on first of adult shell. 



Fig. 3. — Protoconch and first of adult shell of 

 Acmoea sp. showing growth lines, upper edge 

 of adult shell indicated by the arrow. Cam- 

 era lucida, looking at the bottom and one side. 



Fig. -t. — Protoconch of A cmcea sp. 

 a, Sagittal section through cen- 

 tre of shell, on line of be of 

 fig. 1. b, Somewhat oblique 

 section on line ab of fig. 1. 



the middle of the lateral " pouches "' (fig. 3), as may be seen in 

 Morse's fig. 5, although his fig. 4 shows a different condition. 



In sagittal section there is shown merely a csecal-like shell with 

 the suggestion of a coil in the form of the ridge or inner anterior 

 margin of the protoconch (fig. 4a). This appearance is further 

 strengthened by the section of a shell with the animal still within 

 it (fig. 5). The shell in this has been slightly decalcified. By 

 making a somewhat oblique section of one side (fig. 46), a still 



