BRITISH FOSSILS. 



3 



By some accident my name is attached to this species on the plate. 

 Our specimens are those figured and described by Portlock. 



Locality and Geological Position. — Caradoc of Desertcreat, 

 Tyrone. 



Other Species of the Genus. 



I only know one other British species, and no foreign ones. 



S. MTJECHISONIiE, Murch, — S. convexus, trilobus, capite longo semi- 

 ovato, spiiiis prodiictis. Cauda loiiga, axe prominulo IcBvi, 



Synonyms. Ogygia Murchisonice, Murch., Silurian System, 1837, pi. 25, 

 fig. 3. Stygina MurcJiisonicBy Salter in Siluria, 2nd ed. 1859, pi. 4, 

 fig. 1. Morris, Catal. 2nd ed. p. 115, 1854. 



Although only a single specimen of tins has been found, there can 

 be little doubt of the genus to which it should be referred. The 

 contracted axis of the head and body, and the smooth tail with its 

 strong axal lobe, are at all events extremely like those of Stygina. 



Locality. — In Llandeilo Flags ? Mount Pleasant, Carmarthen. 

 It is, however, probable these are Caradoc strata. 



J. W. Salter. 



November 1864. 



Explanation of Plate II. 



Fig. L Portlock's original specimen figured in the Geological Keport on Tyrone. 

 Fig. 2. Dissected head of the same, showing obscure pyriform glabella, its base (a) only 



convex, and part of the striated incurved portion c, c?, continuous with the 



hypostome to the short posterior angle, where it is obliquely folded. At 



h, the termination of the facial suture beneath the eye. 

 Fig. 2. e,f, thoracic rings of the same ; g, tail showing the fulcrum. 

 Fig. 3. Larger specimen (the figured specimen of A. marginatus, Portl.), showing 



impression of the labrum in situ. 

 Fig. 4. Under surface of one of Prof. Thomson's specimens, with broken labrum 



showing concentric lines. 



