4 
William Patten. 
II. Historieal. 
The first specimens of Tremataspis were obtained in Osel in 1853, by Friedrich 
Schmidt. Не turned theni over to C. Pander who, according to Rohon, figured and 
described tlie fragmentary specimens in 1856, as Stigmolepis Owenii, Melittomalepis elegans 
and Odontodus Rootsiküllensis. 
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 itPander’s Cephalaspis Schrenckii. 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 dépréssion, 
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 considérable detail, and he asserts 
with astonishing précision 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 microscopie 
structure of the shield that later observers hâve 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 regulär prismatic spaces, and permeated by a 
System of regularly anastomosing vessels surrounded by concentric bony lamellae 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 1 ), T. Mickwitzi and T. Simonsoni. The micro- 
1) The following interestiag bit of unrecorded history, 
illustrating one of the fnany instances in which the Ostra- 
coderms hâve been mistaken for Arthropods, was related 
to me by Herr Academiker Schmidt. 
In 1853, E. v. Eichwald, the founder of the genus 
Thy estes, described Thyestes verrucosus as a Crustacean, 
but on showing his specimens to Pander, the latter 
pointed out to him the resemblance between Thyestes and 
Cephalaspis, whereupon Eichwald remodclled his manu- 
script and transferred Thyestes from the Crustacea to the 
Vertebrates. 
