﻿JET. S. Williams — Lamellibranchiata and Species-making. 197 



after it. This only complicates the matter, and the 10th of the 

 British Association rules forbids the retention of Microdon. 



The genus Cytherodon Hall, was first figured in 1872 (23d 

 Eeg. Kept., PI. 14, figs 19, 20 and 21), with the name but with 

 no description. The figures, 19 and 20, were Cytherodon iumidus 

 Hall and Nuculites appressus Conrad, and 21 was specifically 

 unnamed. In Plate VIII of generic illustrations, 1882 (publ. 

 1881), figs. 19 and 21 are reproduced, and both are given as illus- 

 tration of the genus Schizodus, and the specific name nasutus is 

 given to the original specimen, figured from a cast in fig. 21. 

 In the final volume the specimens, figured as 19 and 20, are 

 referred to Schizodus, and only the single specimen, represented 

 by fig. 21, is left to represent the genus Cytherodon. Thus it 

 appears that the specimen which ultimately becomes the type 

 and sole representative of the genus Cytherodon Hall, was named 

 and described and referred to the genus Schizodus, after Cythe- 

 rodon was proposed as a genus distinct from Schizodus. 



Conocardium Bronn, has no relation to the Cardiadias, a fact 

 heretofore unknown and brought to light by Dr. Lindstrom and 

 communicated by letter to Prof. Hall. (See note, p. xxxiv). 

 The forms hitherto generally referred to Cardiola are identified 

 with Barrande's genus Panenha. 



The genus Qlyptocardia is proposed for the forms called 

 Venericardium relrostr latum von Buch, Cardium palmatum 

 Gold fuss, Avicula speciosa and Cardiola speciosa Hall. 



Modiella is said to be " in all respects very similar to some 

 recent forms of Modlola." Why then propose a new genus? 



The genus Sanguinolites M'Coy, is discarded for all the species 

 formerly referred to that genus, and only used for two species 

 which formerly were called Edmondia. The species originally 

 called Sanguinolites are distributed among two new genera, 

 Sphenotns and Spathella, and the old genus Orthonota Conrad. 



A glance at the distribution of the Lamellibranchs and their 

 range geologically, discovers the following facts. The species 

 of the Marcellus, Grenesee and Portage groups are mainly found 

 to belong to the same genera, and these genera are rarely found 

 in the Upper Helderberg, Hamilton or Chemung ; and vice versa, 

 the prevailing genera of the Hamilton and Chemung faunas are 

 rarely found in the Marcellus, Grenesee or Portage. A study of 

 the Chemung species shows that the species common in the 

 more western exposures are rare in eastern New York. Of 

 the Dimyaria, the genera beginning in the Hamilton reappear 

 more frequently and abundantly in the Ithaca group and 

 among eastern representatives of Upper Devonian, and in the 

 western sections they do not appear till near the close of the 

 Chemung, or till the Waverly. The characteristic forms asso- 

 ciated with the general Chemung fauna in western New York 



