THE ZOOLOGIST. 
THIRD SERIES. 
Vou. IT.] NOVEMBER, 1878. [No. 23. 
ON SOME PECULIARITIES IN THE ANATOMY OF 
SOFT-SHELLED TURTLES. 
By G. A. StrockwELt, M.D. 
AmonG the remarkable forms which, while preserving a general 
conformity to the typical structure, Nature has impressed upon the 
Vertebrates, none perhaps present greater anomalies than the order 
Testudinata. They have ever attracted attention, and afford rich 
results when they become the subject of anatomical investigation. 
Strange to say, while the Soft-shelled Turtles of the Old World are 
almost exclusively confined to those regions south of the twenty- 
first isothermal, the distribution of their North American repre- 
sentatives is exactly the opposite. 
In the Upper Mississippi Valley, and throughout the Great 
Lake Region, even as high as Athabasca, is found Aspidonectes 
spintfer, Agassiz (Tryonix spinifer of Lesson), which, unlike the 
majority of Tortoises common to this region, presents a peculiar 
conformation of the paws entirely unfitting it for terrestrial loco- 
motion, and only suitable for swimming. Each paw possesses 
three toes, all more or less movable, and joined together as far 
as the nails by broad flexible membranes; and it is by no 
means certain that a fourth toe is not common, though but a 
rudimentary tubercle, as several specimens have been seen with 
this peculiarity. 
The observations of the writer were begun some years since 
under the pupilage of Professor Sager, State Zoologist of Michigan, 
and confined almost exclusively to Michigan and Ontario, where, 
strange to say, the above-named species is common to all the 
3F 
