Raymond — Common Devonian Brachiopods. 279 



Art. XXVI. — The Developmental Changes in some Common 

 Devonian Brachiopods; by Percy E. Raymond. (With 

 Plates XII-XYIII.) 



Introduction. 



Certain layers of impure, clayey limestone from the Mos- 

 cow (Hamilton) shales which occur in a ravine near Canan- 

 daigua Lake, JST. Y., were found by Dr. John M. Clarke to 

 contain fossils whose shells had been so completely replaced 

 by silica that when the rock was etched in acid the shells were 

 left in as perfect condition as when they were buried in the 

 limy clay of their native sea-bottom. A large quantity of 

 this material was obtained by Prof. C. E. Beecher, and through 

 his kindness part of it has been placed at the disposal of the 

 writer for study. About 65 pounds of the rock were treated 

 with hydrochloric acid, and the shells washed from the clay 

 which remained after the calcium carbonate had been removed. 

 From this material about 15,000 nearly perfect specimens have 

 been selected, while a much greater quantity of fragmentary 

 material was discarded. Nearly all classes of invertebrate 

 animals are represented in this collection, but the brachiopods 

 are most numerous, comprising two-thirds of the total number 

 of individuals, and furnishing at least thirty-five hundred speci- 

 mens of a single species (Chonetes seitulus). Next in abun- 

 dance to the brachiopods are the Bryozoa, then the Crustacea, 

 worm tubes, pelecypods, gastropods, corals, and cephalopods, 

 in the order named. The echinoderms are represented only 

 by crinoid columns and the sponges by a few spicules. A few 

 fish scales were also found. Chitinous shells of the Lingula 

 type do not appear to have been preserved, and some of the 

 Dimyarian bivalves occur only as casts. 



The majority of shells are white, but some are dark gray to 

 black, while the trilobite tests are light to dark brown. The 

 color seems to be fairly uniform for all the individuals of the 

 same species. For instance, there are two species of Mono- 

 trypa, and all the individuals of both species are black, yet 

 most of the Bryozoa are light colored. In the case of Chonetes 

 mucro?iatus, however, while most of the specimens are dark, a 

 few are white. 



The state of preservation of the fossils in this material is 

 remarkable, even the finest details being retained, which shows 

 conclusively that the shells were not subjected to any rough 

 wave action after the death of the animal. The graceful 

 fronds of the Fenestellidse are obtained as they grew, and the 

 delicate spines of the Productidse and the spiniform exten- 



