1906.] 



NATURAL SCIENCES OF PHILADELPHIA. 



559 



Fig. 



-G. d. hrittsi, Hot Springs ; series showing changes with growth, X 4. 



subspecies differs from typical Eastern G. demissa chiefly by the usual 

 development at some stage of the internal lamina, whereas we have never 

 seen this structure in any Eastern examples of the species. 



G. d. hrittsi is a more primitive form than G. demissa, and its chief 

 claim to renown is that it supplies the link between the toothed Gas- 

 trodonts, such as G. gularis, and those without teeth, G. acerra, ceri- 

 noidea, ligera and intertexta, with which demissa has hitherto been 

 associated. When young, G. d. hrittsi belongs to the dentate group, 

 but adults qualify to enter another class. *^ 



Like the Gastrodonts of the Appalachians, these Ozarkians vary 

 interminably in minor features with locality. At Magazine Mt., 

 Logan Co., Ark., we took it sparingly at all elevations. Also on the 

 Petit Jean Mts., south of Magazine, where they are 9 to 10 mm. in 

 diam., the young of 5 mm. being laminate. Also on the Poteau Mts., 

 south of Gwynn, Sebastian Co., and on Sugar Loaf Mt., in Indian 

 Territory, west of Gwynn, where those up to three-fourths grown are 

 laminate. 



At Chadwick, Christian Co., Mo., there is a large acerra-like form, 

 diam. 12 mm., with 6^ whorls and coarse sculpture. Only a few were 

 taken, none being of the laminate form. The identification of this lot 

 remains a little uncertain. 



The largest specimens we have seen are from Mena, Polk Co., Ark., 

 where they measure up to 8.5 x 14 mm., with 7 whorls. A young one, 

 7.5 mm. diam., is laminate, as are all those of smaller size. The 



" It may be noted that the ligera group was not included in Gastrodonta by 

 Binney and former authors. It was transferred to that genus by Pilsbry some 

 years ago on anatomic grounds. The conchologic connection is now estabUshed. 



