The Development of Ischnochiton. 569 



This latter phase of the problem I intend to present at another time, 

 paying more particular attention to the development beyond the 

 oldest stages considered in this paper. 



The work was begun in the summer of 1895 at the Hopkins 

 Seaside Laboratory, Pacific Grove, California, and during the following 

 year, so far as my duties would permit, was continued in the zoological 

 laboratory of the Leland Stanford Junior University. In this con- 

 nection it becomes a most pleasant duty to acknowledge my deep 

 indebtedness to the directors of the Hopkins Laboratory, Dr. C. H. 

 Gilbert and Dr. 0. P. Jenkins, for placing at my disposal the 

 exceptional advantages which the laboratory affords. During the past 

 two years the work has been carried on in the zoological laboratory 

 of the University of Pennsylvania, under the direction of Professor 

 E. G. CoNKLiN, to whom I cannot adequately express my appreciation 

 of his many kindnesses. And I am particularly indebted to my wife 

 who has rendered me great assistance. 



Ischnochiton magdalenensis. 



I. Natural History, 

 The material for this work was collected at the Hopkins Seaside 

 Laboratory on Monterey Bay, California, about 120 miles south of 

 San Francisco. The north and east shores of the bay are sandy, but 

 upon the south a granite formation breaks through the cretaceous 

 conglomerate and rises above the sea level from ten to fifty feet. The 

 clift's, together with the outlying islands, support innumerable plant 

 and animal forms. Not less than twenty species ' ) of Chiton occur in 



1) Professor Pilsbey, of the Academy of Sciences, Philadelphia, 

 has kindly identified the following species collected in Monterey Bay: 



Lepidopleuridae. 

 Lepidopleurus rugatus Cpr., L. nexus Cpr. 



Ischnochitonidae. 

 Tonicella lineata Wood, Trachydermon (Cyanoplax) raymondi 

 PiLS. , T. {Cyanoplax) hartwegi Cpr., Ischnochiton radians Cpr., 

 I. scahricostatus Cpk. var., I. regularis Cpr. , I. mertensi Midd., 

 /. cooperi Cpr., I. (decipiens var. ?) sinudentatus Cpr., /, (Stenoradsia) 

 magdalenensis Hinds, Gallistochiton crassicostatus Pils., C. palmulatus 

 var. mirahilis Pils., Chcetopleura gemmea Cpr., Nuttallina californica 

 'NuTT.' RvE., JV", thomasi Pils. 



37* 



