Historical SkelcJ) oj Classifications 43 



7iiti(lu.s and F. fontdnus because of the presence of the flagella on the penis. 

 This is, as far as known to the writer, the first attempt to chissify the 

 Planorbidae by reference to details of the anatomy. 



In 1891, Buchner pubHshed the first comprehensive account of the 

 genitalia of the family Planorbidae. He divided the male organ into four 

 types, (1) corneus with a small penis, (2) nitidus and cotnplanatus with 

 flagella and sperm outlet at the side, (3) marginatus and carinatus with 

 sperm outlet in the center, and (4) contortus, vortex, rotundatus, and albus 

 with a stylet. He did not distinguish the peculiar gland of corneus from 

 the penis. The difference between the prostate diverticula of Planorbis 

 corneus and the smaller species, vortex, carinatus, nitidus, etc., w'as espe- 

 cially mentioned but no reference was made of the presence of a separate 

 prostate duct. There was a good account of the excretory organ (kidney). 

 Simroth's account (1912) of the genitalia of the Planorbidae was based on 

 Buchner's work and added nothing to our knowledge of the antomy of the 

 group. 



In 1917, L. Soos published a paper on the anatomy of the Hungarian 

 Planorbidae, giving figures of the genitalia of Planorbis corneus, Tropidis- 

 cus planorbis, Segmentina nitida, Bathyomphalus contortus, Gyrorbis 

 spirorbis, and Gyraulus albus. The radulae and the digestive system were 

 also considered. This is the best work on the anatomy of the Planorbidae 

 which had appeared up to this time. 



During the decade from 1921 to 1930, several notable papers appeared 

 on the anatomy of the family. Annandale (1922) and Annandale and 

 Prashad (1919-1921) added to our knowledge of the anatomy of the 

 Indian Planorbidae. In 1923, Rao published an exhaustive treatise on the 

 anatomy of Annandale's new genus Indoplanorbis. Connolly (1925) figured 

 the genitalia and radula of Planorbis pfeiffen which indicated that it was 

 related to the West Indian genus Tropicorbis. F. C. Baker, in 1926, pub- 

 lished notes on the genitalia, jaws, and radulae of certain American 

 Planorbidae and in 1928 (AIolI. of Wis., I, pp. 306-387) presented descrip- 

 tions and figures of the genitalia, jaws, and radulae of the species of Pla- 

 norbidae inhabiting the Middle West. The subfamily Helisominae (Heli- 

 somatinae) was proposed as new on page 309 of that work. The classifica- 

 tion of the genitalia is based on that of Buchner with the addition of two 

 types, one new and one following Annandale. 



In 1929, Odhner published an account of the Alollusca of the Tiikerns 

 in which the genera were separated by characteristics of the genitalia, 

 radulae, and other anatomical features. On page 22 a key appeared in 

 which the groups were briefly diagnosed from the anatomical standi)oint. 

 This was the most modern treatment which the family had received and the 

 key is the first attempt to separate the genera by the use of anatomical 

 differences. 



During the decade 1931 to 1940, several critical papers appeared on 

 the anatomy of the Planorbidae, adding greatly to our knowledge and 

 clearing up many doubtful jioints in the classification based on the anato- 

 my. In 1931, Germain issued his work on the land and fresh-water mol- 

 lusks of France in which outline figures of the genitalia, and some of the 

 radulae, were given. No attempt was made, however, to base a classifica- 

 tion on the anatomical data. Also in 1931, appeared F. C. Baker's paper 



