ABSTRACTS AND DISCUSSIONS OP PAPERS 147 



or less reduced, but may often be still recognizable in the interior mold as a 

 pit, due to the inward growth of the lenslike thickening of the crust. Per 

 contra, it is most strongly developed in the so-called "blind" trilobites, where 

 the lateral eyes are reduced or lost. The more important Cambric families 

 still lack the eye tubercle, but in young specimens of Elliptocephala asaplioides 

 the median eye was found to possess the primitive forms of two separate trans- 

 parent spots or lenslike thickenings on the front part of the glabella that do 

 not project above the surface. 



It has been recognized by zoologists for some time that the trilobites nor- 

 mally should possess median or parietal eyes. 



The "ocelli" of Harpes, Cryptolithus, and Dionide are reduced lateral eyes 

 with traces of the true suture. 



Following Doctor Buedemann's paper was one on the general subject 

 of reef deposits, which brought forth a discussion, participated, in by 

 Messrs. Ulrich, Van Ingen, Schuchert, Berry, and the author. Illustrated 

 by lantern slides ; 20 minutes. 



IMPORTANCE OF "CORAL REEFS" AND REEF DEPOSITS IN THE FORMATION 

 OF PALEOZOIC LIMESTONES 



BY THOMAS C. BROWN 



(Abstract) 



In the Paleozoic limestones a number of coral reefs and reef-like structures 

 have been described from various horizons. In the present-day reef areas it 

 has been found that a large part of the calcium carbonate deposited is pre- 

 cipitated chemically by reactions brought about by micro-organisms. There 

 are many Paleozoic horizons where similar conditions prevailed. This is 

 clearly shown by the nature of the sediments and by the structural relations 

 of the strata thus formed. 



Many of the Paleozoic limestones which have generally been considered to 

 be the products of the mechanical attrition of shells and other organic struc- 

 tures, or of the disintegration of preexisting limestones, show by their internal 

 structure and physical features that they were formed under conditions similar 

 to the reefs of today. 



The following paper on the distribution of corals was next in order 

 and was discussed by Messrs. Ulrich, J. M. Clarke, Van Ingen, Ami, and 

 the author; 20 minutes. 



DISTRIBUTION AND INFERRED MIGRATION OF AMERICAN MIDDLE AND 

 UPPER DEVONIC CORALS 



BY ASIAUEUS W. GRABAU 



(Abstract) 



While monographing the Michigan Devonic corals light was obtained on the 

 probable routes of migration between America and Eurasia, these being appar- 

 ently across the North Polar region during Onondaga time and via Alaska and 

 the northwest Canadian region subsequently. 



