2 
William Patten. 
When, tlierefore, through the generosity of thc administration of Dartmouth College, 
I was granted a half year’s leave of absence, for scientific work, I decided to make as thorough 
an investigation of the Ostracoderms as my time and means would allow, with the special 
object of determining whether any evidence could be fouud beariug ont oui* a priori as- 
sumption that they are an intermediate group of animais, related on one liand with the 
Arthropods and on the otlier with the Yertebrates. My plan was to study all thé most im¬ 
portant collections in Great Britain and the continent, and to purchase, or collect, material 
that might be used for detailed study by sectioning or by otlier methods, as the valuable 
type specimens permanently preserved in Museums could not be utilized in tins manner. 
In pursuance of this plan, I visited and studicd the valuable collections of Ostra¬ 
coderms at Edinburgh, London, Oxford and Cambridge, Berlin, Levai, St Petersburg and 
Stockholm. 
I desire to express my gratitude to the officiais of these institutions for the immédiate 
and abundant assistance they hâve given me in the undertaking. I am under special obli¬ 
gation to Prof. R. H. Traquair for some valuable photographe of Gephalaspids , and to 
Mr. W. E. Clark for Ins personal assistance in the examination of the collections in the 
Museum of Arts and Sciences at Edinburgh; to Dr. Smith Woodward for the great pains 
lie lias taken to facilitate my work at the British Museum; to Prof. Sollas of Oxford for 
the privilège of sectioning and making a special study of some valuble heads of Pteraspis 
and Gephalaspis ; to Dr. Otto Jäckel of Berlin and Dr. E. J. G. Holm of Stockholm and 
J. Tolmatschow of Petersburg for many favors that hâve aided me in my work. Finally, 
it gives me special pleasure to acknowledge my appréciation of the innumerable ways in 
which Herr Academiker Schmidt of St. Petersburg, by bis ever genial and kindly personal 
advice and assistance, not only aided me to the füllest extent possible in my scientific work, 
but made my two months in Petersburg a most delightful and never to be forgotten sojourn. 
It did not take long to discover that the following out of the second part of my pro- 
gram, the collection of Thyestes and Tremataspis , was a most difficult task. So far as I 
know, every fragment of these two généra lias been taken from a shallow pit about four feet 
deep, and covering perhaps an area of three or four hundred square yards, hidden in the 
heart of the reinote and otherwise little known island of Ösel in the Baltic sea. The myste- 
rious treasures of this classic spot hâve drawn to its sides many famous scientific men from 
all quarters of the globe. 
From time to time during the last forty years or more, many beautifully preserved 
Eurypterids ,' and an occasional Tremataspis , hâve been taken from this insignificant pit in a 
pasture. During the past twelve or thirteen years, the spot lias been worked with skill and 
systematic energy by Mr. A. Simonson, who lias collected, with very few exceptions, ail 
the material of Tremataspis and Thyestes that lias ever been found. And yet with the most 
careful aud painstaking work, and with considérable assistance from common laborers, two 
or three, very rarely four, fragmentary heads of Tremataspis are ail that reward the labors 
