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FS SLAS) 
14 G. LINDSTRÖM, A SILURIAN CYATHASPIS FROM GOTLAND. 
Explanation of Plates. 
The signification of these letters is identical in all figures. 
Interior or basal stratum (nacreous lamellae of A. SMITH-W0O0ODWARD, 
die Osteoide Schicht of ROHON). 
The vacuole stratum (wmiddle substance with cavities HUXLEY, pris- 
matic layer SALTER, middle cancellated polygonal cells LANKESTER, 
Mittlere Schicht ZITTEL, polygonal cancellze S. WOODWARD, Me- . 
dullarräume ROHON). 
Partition walls between the vacuoles. 
Haversian canals according to ROHON. 
Pulpa canals. 
Dentine tubuli (Reticular layer with diverticula HUXLEY, External 
finely striated layer LANKESTER, Dentinrörchen ZITTEL, vaso-dentine 
S. WOODWARD, Dentin ROHON). 
Enamel ridges of the exterior surface. 
Crenated ledge of a ridge. 
The open grooves between the ridges. 
Plate I. 
Fig. 1. The dorsal scutum, maguified ?/4. The faintly shaded 
portion of the rostral plate lies under the anterior edge of the ventral 
shield. The pointed lines to signify the presumed hidden outlines of 
the shield. 
Fig. 2. Part of the same, where the rostral plate, the central 
disc and the left cornu meet. Elås 
Fig. 3. The right posterior end ” of the dorsal scutum, from 
the side, also with the posterior end of the right cornu "", 4. 
Fig. 4. Anterior part of the left cornu, showing the notch of 
therorbit.= s/s 
Fig. 5. The ventral seutum. ?/,. 
Fig. 6. Scale in natural size. 
Fig. 7. "Tbe same magnifed. 37 
3. Impression of another scale, nat. size. 
Fa 195 IExoskeletont ot atlimabytes 
Fig. 10. Section of the larger end of the same. 
Fig. 11. Section of the narrow end of the same. 
Fig. 12. Part of the interior surface of the same, showing the 
tubes and basal lines of the vacuole walls. $/. 
