708 A CENTURY OF PROGRESS IN THE NATURAL SCIENCES 



tremata, have arisen. The classification shows that for the genetic relationships 

 use was made of all parts of the hard anatomy. 



In the interval between 1910 and 1932 significant advances were made in the 

 classification of certain Upper Paleozoic brachiopods, with emphasis on the in- 

 ternal structures as viewed under the microscope in thin section, 'in 1910 Ivor 

 Thomas published an important memoir on the British Carboniferous Ortho- 

 tetinae and in 1914 a memoir on the British Carboniferous Producti, in which 

 a special terminology was introduced for the investigation of the shells of species 

 which had been collectively grouped under the name Productus. As a result 

 several species were separated from Productus and placed in four newly created 

 genera. In 1910 Stoyanow placed the species typica with a vertical partition in 

 the pedical valve in a new genus Tschernyscheivia. G. S. Girty, also in 1910, 

 described the species elegans with a transverse partition under the new genus 

 Diaphragmus. However, a detailed study of the original material of Productus 

 productus (Martin) by Muir-Wood in 1928 revealed that that species also pos- 

 sessed a transverse partition and, according to the rules of priority, Diaphragmus 

 was placed in synonymy by Dunbar and Condra in 1932. The discovery made 

 by Muir-Wood resulted in the elimination from the genus Productus of a vast 

 number of species with vertical partitions and the erection of twenty-nine new 

 genera and subgenera by Dunbar and Condra. The genus Productus in its re- 

 stricted usage occurs only in the Lower Carboniferous. Other important contri- 

 butions have been made by Stuart AVeller (1914) and Th. Tschernyschew (1902). 



Pelecypoda and Gastropoda: These organisms have become increasingly 

 abundant in number of genera and species during the course of geologic time, 

 reaching their acme during the Tertiary and Recent. They are thus important 

 to the geologist concerned with the later geologic periods. The advances made 

 in the science of conchology have been intricately associated with the investiga- 

 tions of fossil shells, although the classifications are based largely on the mor- 

 phology of the soft parts. In general, paleontologists have adopted some of the 

 broader groupings of families and subfamilies used by zoologists, but the de- 

 scriptions of genera and species deal almost entirely with the morphological 

 characters of the hard parts. 



By the middle of the nineteenth century there had been described and illus- 

 trated a vast number of genera and species, both fossil and living, and to enu- 

 merate all the important authors would exceed the limited scope of this review. 

 In the first half of the century the works of Lamarck on the Tertiary mollusks 

 of the Paris Basin and the early, work of Paul Deshayes (1824-1837) presented 

 a classification and laid the foundation for further molluscan research in both 

 Europe and America. Other contemporaneous investigators included the G. B. 

 Sowerbys (father and son), Schlotheim, and Goldfuss. By the middle of the 

 century many investigations were undertaken which resulted in monographic 

 studies of special groups of mollusks as well as of faunas obtained from particu- 

 lar formations. 



Among the important publications concerned with the morphology and clas- 

 sification of molluscan groups is that of P. Pelseneer (1906) which devotes spe- 

 cial attention to the gills. These characters can be used only with living forms 

 but the groupings of genera based on that kind of information compares well 

 with other classifications founded on a study of the shell characters. In 1884 



