Charles Emerson Beecher. 417 



and from the former descended the Protremata (Strophome?ia, 

 ProductuS) etc.). 



One of the clearest cases of parallelism between the ontogeny 

 and phylogeny in a group of invertebrates was described by 

 Beecher. Living species of the family Terebratellidse have 

 a very wide distribution, and he showed that the highest genera 

 of the austral forms " pass through stages corellated with the 

 adult structure in the genera Gwynia, Oistella, B our char dia, 

 Megerlina, Magas, Magasella, and Terebratella, and reach 

 their final development in Magellania." In the forms having 

 a boreal distribution the metamorphoses corellate " with adult 

 structures of Gwynia^ Cistella, Dlatidia, Ismenia, Muhl- 

 feldtia, Terebratalia, and Dallina. The first two stages in 

 both subfamilies are related in the same manner to Gwynia and 

 Cistella. The subsequent stages are different except the last 

 two, so that the Magellania structure is similar in all respects 

 to the Dallina structure, and Terehratella is like Terebr alalia. 

 Therefore Magellania and Terebratella are respectively the 

 exact morphological equivalents to, or are in exact parallelism 

 with Dallina and Terebratalia. 



u In each line of progression in the Terebratellidse, the 

 acceleration of the period of reproduction, by the influence of 

 environment, threw off genera which did not go through the 

 complete series of metamorphoses, but are otherwise fully 

 adult, and even mav show reversional tendencies due to old 

 age ; so that nearly every stage passed through by the higher 

 genera has a fixed representative in a lower genus. Moreover, 

 the lower genera are not merely equivalent to, or in exact par- 

 allelism with, the early stages of the higher, but they express 

 a permanent type of structure, as far as these genera are con- 

 cerned, and after reaching maturity do not show a tendency to 

 attain higher phases of development, but thicken the shell and 

 cardinal process, absorb the deltidial plates, and exhibit all the 

 evidences of senility." 



In 1893 there was discovered in the Utica formation near 

 Rome, New York, a thin band not more than one- fourth of an 

 inch thick, in which nearly all the fossils preserved (Triarihrus 

 and Trinucleus) occur as pseudomorphs in iron pyrite, and 

 retain antennae and legs. Specimens of trilobites with legs 

 had been known before in two specimens, and in four genera 



