2 William Patten. 



When, therefore, through the generosity of the 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 found bearing out our a priori as- 

 sumption that they are an intermediate group of animals, related on one hand with the 

 Arthropods and on the other with the Vertebrates. My plan was to study all the most im- 

 portant collections in Great Britain aud the continent, and to purchase, or collect, material 

 that might be used for detailed study by sectioning or by other methods, as the valuable 

 type specimens permanently preserved in Museums could not be utilized in this manner. 



In pursuance of this plan, I visited and studied the valuable collections of Ostra- 

 coderms at Edinburgh, London, Oxford and Cambridge, Berlin, Reval, St Petersburg and 

 Stockholm. 



I desire to express ray gratitude to the officials of these institutions for the immediate 

 and abundant assistance they have given me in the undertaking. I am under special obli- 

 gation to Prof. R. H. Traquair for some valuable photographs of Gephalaspids^ and to 

 Mr. W. E. Clark for his 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 

 he has taken to facilitate my work at the British Museum; to Prof. Sollas of Oxford for 

 the privilege of sectioning and making a special study of some valuble heads of Pteraspis 

 and Gephalaspis; to Dr. Otto Jackel of Berlin aud Dr. E. J. G. Holm of Stockholm and 

 J, Tolmatschow of Petersburg for many favors that have aided me in my work. Finally, 

 it gives me special pleasure to ackuowledge my appreciation of the innumerable ways in 

 which Herr Academiker Schmidt of St. Petersburg, by his ever genial and kindly personal 

 advice and assistance, not only aided me to the fullest 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 genera has 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 remote and otherwise little known island of Osel in the Baltic sea. The myste- 

 rious treasures of this classic spot have 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, have been taken from this insignificant pit in a 

 pasture. During the past twelve or thirteen years, the spot has been worked with skill and 

 systematic energy by Mr. A. Simonson, who has collected, with very few exceptions, all 

 the material of Tremataspis and Thyestes that has ever been found. And yet with the most 

 careful aud painstaking work, aud with considerable assistance from common laborers, two 

 or three, very rarely four, fragmentary heads of Tremataspis are all that reward the labors 



