D1THYR0CARIS TRICORNIS. 175 



retaining the carapace whole, having its dorsal and two mesolateral ridges, and 

 other characteristic features, including a reticulate and subaculeate ornament of 

 the surface. 



Compare PI. XXII, figs. 5 d, e (for the ornament) ; PI. XXIV, figs. 5 a, h (for 

 shape and outline). 



This well-preserved specimen clearly exhibits the clypeiform test, with its 

 dorsal convexity (fig. 4 b), when looked at sideways, and its suboblong and 

 angulate shape when viewed from front or behind (figs. 4 c, d). Its dorsal 

 ridge and ornament are magnified in fig. 4 e. 



From Kirkton holme, East Kilbride. 



PL XXV, figs. 9 a— c. Mus. Geol. Surv. Scotland, F -f-, No. 20. 



This is a large separate dorsal ridge, possibly belonging to D. tricornis or 

 D. Colel, or even to a different species. 



Size. — Length probably about 60 mm. when perfect ; width in the middle 

 5 mm. 



Characters. — A long, narrow, fusiform, rugose ridge, with a flat narrow flange 

 along each side. Thus it matches such a dorsal ridge as belongs to D. tricornis 

 (PL XXIV, figs. 1 and 6) or D. Colel (PL XXIV, fig. 2). The latter seems to 

 have had a rather longer carapace and ridge than the former, but its ridge is not 

 so thick. 



The rugosity of fig. 9, PL XXV, has a slight difference of structure from that 

 of the other rugose ridges (PL XX, figs. 2 b, 3 g), due to the divisions of the 

 chevrons being more exactly alternate in their distances and in their extent over the 

 ridge, so that there appears to be almost a double row of rounded rugae along this 

 ridge. This, however, may have been the character of an individual, not of a 

 species (see D. granulata, PL XX, figs. 2 b and 3 g). 



In brownish calcareous shale. From the Calciferous Sandstone group at 

 Larriston Burn, near New Castleton, Roxburghshire. 



If this dorsal ridge belonged to either D. tricornis or D. Colei, both species are 

 also represented in the Roxburghshire beds. 



PL XXV, figs. 10 a—c. Mus. Geol. Surv. Scotland, F - x ^, No. 20. 



The surface of the piece of hard shale in which the foregoing dorsal ridge is 

 embedded is covered with scattered carapaces of small Ostracoda, mainly if not 

 entirely belonging to Kirkbya plicata (figs. 10 a, side view ; 10 b, edge view ; and 

 10 c, end view). 



My friend Mr. J. W. Kirkby tells me that from this locality (Larriston Quarry) 

 the Geological Surveyors of Scotland have obtained several good sets of Ostracoda, 

 which he has determined as Leperditia Okeni (and varieties), Kirkbya costata, K. 



