William Patten. 



11. Historical. 



The first specimens of Tremataspis were obtained in Osel in 1853, by Friedrich 

 Schmidt. He turned them over to C. Pander who, according to Rohon, figured and 

 described the fragmentary specimens in 1856, as Stigmokpis Owenii, Melittomalepis elegans 

 and Odontodus Bootsikiillensis. 



In 1866 (Verhandlungen der Mineralogischen Gesellschaft, neue Serie, Bd. I. p. 233) 

 F. Schmidt established the genus Tremataspis on some well preserved material, and in- 

 cluded in it Pander's Gephalaspis SchrencMi. Schmidt gave an excellent description of the 

 general form and structure of the shield. He also described the Crista occipitalis and the 

 pores and tubercles as seen from the surface of the shield ; the anterior median depression, 

 or «Kreiswulst» with its longitudinal fissure, that he compares with a nasal pit; the eyes, in 

 a common «biscuit-shaped» opening; the oval post-orbital opening; the two minute openings 

 still further back; and the lateral oval openings between the eyes and the margin of the 

 shield. The anterior margin of the ventral shield, with its large median projection, and the 

 five pairs of small lateral serrations, are described in considerable detail, and he asserts 

 with astonishing precision that the large opening in front of the ventral shield was probably 

 occupied by one or more unknown plates, which were inserted on the free anterior margin 

 of the ventral shield. 



Schmidt gives such a thoroughly accurate and detailed description of the microscopic 

 structure of the shield that later observers have been able to do little more than confirm 

 his account. According to his observations the shell consists of an inner layer of isopedin; 

 a middle one of loose bony tissue surrounding regular prismatic spaces, and permeated by a 

 system of regularly anastomosing vessels surrounded by concentric bony laniellae and 

 numerous lacunae; the third, or outer, layer consists of a ganoid-like epidermis. 



In 1892, Rohon gives a renewed description of the genus, adding numerous details 

 and describing three new species: T. Schmidti'^), T. Mickwitzi and T. Simonsoni. The micro- 



1) The following interesting bit of unrecorded history, 

 illustrating one of the many instances in which the Ostra- 

 coderms have been mistaken for Arthropods, was related 

 to me by Herr Academiker Schmidt. 



In 1863, E. y. Eichwald, the founder of the genus 

 Thyestes, described Thyestes verrucosus as a Crustacean, 



but on showing his specimens to Pander, the latter 

 pointed out to him the resemblance between Thyestes and 

 Cephaluspis, whereupon Eichwald remodelled his manu- 

 script and transferred Thyestes from the Crustacea to the 

 Vertebrates. 



