714 ^ CENTURY OF PROGRESS IN THE NATURAL SCIENCES 



stages of Trilobites he described the simple characters of the protapsis and the 

 changes which it underwent during the development of the Trilobite. He showed 

 that in the earlier Cambrian genera this stage is simple but that in the later, 

 more complex genera by a process of acceleration certain characters have been 

 advanced until they appear in the protapsis. He also pointed out that the ven- 

 tral position of the free checks in the earliest larval stages of all except the 

 highest Trilobites is evidence of low rank and for this group he proposed the 

 name Hypoparia. Of the remaining Trilobites, those in which the free cheeks 

 include the genal angles, he placed in the order Opisthoparia and those in which 

 the sutures cut the lateral margins of tlie cephalon he designated Proparia. These 

 three orders, with some additions and refinements, are in general use at the 

 present time. Further evidence was presented to show that the eyes have mi- 

 grated from the ventral side over the margin and then posteriorly across the 

 cephalon to their adult position. Other changes were noted in the character of 

 the glabella and the segments of the pleura. Beecher emphasized the erroneous 

 earlier interpretations of the Trilobites as closely related to the living Limulus. 

 They lack the operculum of the Limulus and possess primitive crustacean af- 

 finities in their protonauplius larval form, slender jointed antennules, the hypo- 

 stoma and metastoma, five pairs of cephalic appendages, and the biramel charac- 

 ter of the limbs. H. M. Bernard in his paper on the systematic position of the 

 Trilobites in 1895 concluded that the crustaceans originated by the bending 

 under to the ventral side of the anterior segments of an ancestral carnivorous 

 annellid. Other significant papers have been published by C. D. "Walcott on 

 Cambrian Trilobites from 1881 to 1916, in which many new species have been 

 described and illustrated. One of these in 1911 is devoted to a discussion of 

 the Cambrian species of China. 



The Eurypteriids of the Middle Paleozoic were studied by several authors 

 in Europe and North America. F. Koemer in 1848 pointed out their relation- 

 ship to the living Limulus. Other contributions dealing with this group are 

 those of J. M. Clarke and R. Euedemann, who in 1912 described the forms from 

 New York State. The Ostracods, because of their importance in stratigraphic 

 studies, have been investigated by C. I. Alexander (1933), and by R. S. Bassler 

 and B. Kellett (1934), and many others. The fossil Decapods from both the 

 east and west coasts of North America and Central America were described by 

 M. J. Rathbun from 1918 to 1935. 



Fossil insects occur in certain rocks where conditions for preservation were 

 favorable and were described about one hundred years ago by E. F. Germar 

 from Carboniferous formations near Halle, Germany, and by C. Brongniart 

 from rocks of similar age at Commentry. The Lithographic Shales at Solenhofen 

 also have furnished well preserved fossils, which w^ere described by Meunier, 

 Oppenheim, and Munster. S. H. Scudder in 1879 published an important paper 

 on Paleozoic cockroaches and later (1886) an index to the known fossil insects 

 of the world. In 1900 he described the insects of the Florissant shales of Colo- 

 rado. Other important contributions during the past fifty years include a re- 

 view of American Paleozoic insects by A. Handlirsch in 1906, a monograph by 

 Petrunkevitch (1913) on terrestrial Paleozoic Arachnida of North America, and 

 numerous papers by R. J. Tillyard, including his contribution (1923-1934) on 

 the evolution of the class Insecta. 



