BIHANG TILL K. SV. VET.-AKAD. HANDL BAND 21. AFD. IV. N:0 8. 9 
tion with the ambient medium only through a narrow slit-like 
opening left between the opposite ledges of the adjoining 
ridges. 
There can be no doubt that these interesting relics be- 
long to the Cephalaspide in HuxLEY's!) conception or to 
the family of the Pteraspide in the subelass of Ostracodermi, 
ordo Heterostraca, according to A. SMITH-W?00DWARD. ?) 
In comparing this Gotland fossil with others previously 
known there is none with which it may more aptly be identi- 
fied than with Cyathaspis Schmidtii, described by Prof. E. 
GEINITZ, 3) who had the kindness to send me casts of his spe- 
cimen. It is a little smaller than mine, but the shape of 
the scutum and the arrangement of its component parts as 
well as the form of the ridges so nearly coincide in both, 
that the trifling differences as to size may have value only 
as marking varieties. How far these specimens — the German 
and the Swedish — may be justly included in the genus 
Cyathaspis must depend solely upon future discoveries, show- 
ing that the English and other foreign species constituting 
the genus Cyathaspis, have a histological structure similar 
to that of my specimen. So far as I am aware there does 
not exist a single figure of any section published, showing 
the microscopic structure of the scutum in the English and 
Galician specimens. Dr JAEKEL of Berlin has kindly told me 
that »Pteraspis» integra of KUNTH comes very near to my 
specimens in respect of the structure of the ridges, which 
is quite different from that which prevails in the English 
species of Pteraspis as may be seen by comparing with them 
the figures given by LANKESTER ?) and as also sections I have 
taken from such specimens show. »Pteraspis» integra differs, 
however, so much from Cyathaspis and still more from Pter- 
aspis that Dr JAEKEL considers it to form a new generic type. 
Some uncertainty must also prevail” '"”ong as it is not 
known whether or not the specimens of Cyathaspis Schmidtii 
are marked on the interior surface of the dorsal scutum with 
1) Memoirs Geol. Survey Un. Kingdom, British Organ. Remains, Decade X, 
KID. 
5 2) Catalogue of the Fossil Fishes in the British Museum, pt II, p. 159. 
> 3) »Ueber ein Graptoliten-fiöhrendes Geschiebe mit Cyathaspis von Rostock> 
in Zeitschrift der Deutschen geologischen Gesellschaft 1884, p. 854. 
- 2) Monograph of the Fishes of the Old Red Sandstone of Britain, pt I 
plate VII, figs 1—7. 
