﻿1851.] MURCHISON — SILURIAN ROCKS OF SCOTLAND. 



177 



It is concentric and massive, while its muscular attachment to the 

 shell is secured by a long and stout process from its inner surface, 

 near the upper edge. This peculiar form of operculum will at once 

 give generic rank to Maclurea. 

 Locality. Aldeans limestone. 



Orthoceras Barrandei, n. sp. Pl. IX. fig. 19. 



Short, tapering at an angle of 40°; acute at the extremity; the 

 mouth broad and very oblique, surface covered by regular, close 

 ridges of growth, which are not waved, but pass obliquely across 

 parallel to the mouth ; septa in the same direction, occupying half 

 the length of the shell, and about one- sixth their diameter apart. 



This shell is named in honour of the accomplished M. Barrande, 

 who is engaged in figuring some hundreds of Cephalopods from strata 

 of this age. He informs us he has several of this character, and 

 some even more widely conical. 



Locality. Mulloch Quarry. 



Orthoceras vaginatum, Schloth. ? Pl. X. fig. 7. 



Orthoceratites vaginatus, Schlot., De Vern. Geol. Russia, vol. ii. 

 pl. 24. fig. 6. 



Our shell shows the transverse coarse striae, but only indistinct 

 traces of the annulations which occur on this curious Northern spe- 

 cies ; but as that circumstance alone would not be sufficient to di- 

 stinguish it, we adopt the name. The oblique raised lines at each 

 constriction of the siphon are due to the edges of the septa, which, 

 according to De VernemTs excellent figure of O. duplex, a closely 

 allied species, pass down in the siphon through the space of several 

 septa, so as to form a sheathed tube like that of Nautilus sipho. 



Locality. Ardwell. 



EXPLANATION OF PLATES VIII. IX. AND X. 



PLATE VIII. 



Fig. 1. Cheirurus gelasinosus. Portl. sp. Craig Head. 

 Fig. 2. Asaphus (Isotelus), sp. Bogang. 



Figs. 3 a, 3 b. Terebratula, sp. Very like some from N. America. Craig Head, 



Figs. 4 a, 4 b. Orthis virgata, Sow. Bogang, Knockdolian. 



Fig. 5 a. Orthis confinis, Salter ; ventral valve and its interior cast. 



Fig. 5 b. The same ; interior cast of the dorsal valve. 



Fig. 5 c. The same ; hinge-area. 



Fig. 6 a. Pleurorhynchus dipterus, Salter, var. rhomboideus ; side view, with the 



spine indicated, as in Irish specimens. 

 Fig. 6 b. The same ; edge view. 



Fig. 6 c. The same ; middle part of the valve magnified. 



Figs. 7 a, 7 b. Maclurea, sp. (M. magna of Prof. M'Coy's list). Aldeans. 



PLATE IX. 



Fig. 1 a. Calymene Blumenbachii, Brongn.; small specimen. Drummuck. 



Fig. 1 b. The same ; the emarginate hypostome attached beneath the head of a 



larger specimen. Drummuck. 

 Fig. 2 a. Phacops Stokesii, Milne-Edw. sp. Mulloch Quarry. 



