28 THE NAUTILUS. 



apex. In all other North American species the apex is the point of 

 greatest altitude, but in excentricus, the highest point of the shell is 

 anterior to the apex. 



There is some question as to the specific validity of this form. 

 Bourguignat (J. de C. iv, p. 175) considered it to be only a variety of 

 A. radiatus Guilding, characterized by the apex being slightly more 

 acute. And in this, he has been followed by Clessin (Conch. Cab., 

 Ancylus, p. 67). Crosse and Fischer (Miss. Sci. Mex., ii, p. 37) 

 state that it differs from radiatus by its thinner shell, more pointed 

 and more excentric apex and the absence of the radiating striae, and 

 on this account prefer to recognize it as distinct, although admitting 

 that the two forms are very dose to each other. Von Martens (Biol. 

 Cent. Am., p. 402) also describes the shell as "without radial sculp- 

 ture " and considers it distinct. Pilsbry, in his notice of the New 

 Braunfels specimens, however, mentions slight indications of most 

 delicate riblets radiating from the apex. All of the five specimens 

 from Barton Creek have the radial ribs more or less developed. In 

 most of them the ribs are stronger along the antero-lateral slopes, the 

 median portion being nearly smooth or only slightly rippled. In one 

 example, however, the well-developed ribs extend over the entire 

 anterior slope. 



Under these circumstances, the approximation of the Texan shells 

 to A. radiatus seems very probable. Whether this is also the case 

 with the typical form from Guatemala, must remain uncertain until 

 authentic material can be critically studied. I have not been able 

 to make any comparison of the Texan specimens with radiatus. 



V. ANCYLUS PENINSULA Pilsbry & Johnson (1896). PI. II, 



figs. 19-21. 



This beautiful species, which is readily distinguished by "its large 

 size, broadly oval and depressed form, blunt apex and the dense radial 

 striation," is apparently peculiar to the inland waters of Florida, 

 where it seems to be very generally and abundantly distributed. In 

 addition to the original locality, the St. John's River, specimens have 

 been seen from Volusia and Manatee counties and from Lake Jessup, 

 which indicate a general range over the state. It is possible that 

 some of the localities cited by Dall for A. obscurus (Proc. U. S. Nat. 

 Museum, 1885, p. 273) belong to this species. 



