BRITISH FOSSILS. 



3 



STAJJROCEPH ALUS GLOBICEPS. 

 PI. V. Fig. 6. 



Synonyms. Ceraurus glohiceps, Portlock (1843), Geol. Rep., Tyrone, 

 257, t. i. f. 7. Staurocephalus globiceps, Salter, in Morris's Catal., 

 2nd ed. (1857), p. 115. 



Diagnosis. S. ovatus granosus, cauda elongata, spina iitrinque unica 

 divergenti. Glabella siipite brevi vix lobato. Oculi approximati. SpincB 

 genales et pleurales diffnsce. Cauda brevis^ pleuris primariis longe 

 extensis, latis ; reliquis — ? 



A much smaller species than the preceding, and distinct from it 

 by abundant characters of shape and habit. The divergent spines 

 of head, thorax, and tail enable us at once to recognize it ; and of 

 the latter, the remarkable extended first pair of pleurae (the rest of 

 the tail is lost) show a near connexion Avith the S. ?■ Maclareni, 

 afterwards described. 



Only one good specimen, 10 lines long, is known. The head is 

 equal to the thorax in length, and longer than the caudal portion. 

 It has a very large globular front, longer thaji the square stipes, 

 and granular all over. This stalk or base seems to be without 

 furrows. The cheeks granular, gibbous, witli a prominent eye on 

 the front edge, near the glabella, and directed forward, not outward ; 

 a broad plain margin, and widely divergent spines. 



The axis of the thorax is cylindrical, and as wide as the stalk of 

 the glabella. The pleurae flat as far as the fulcrum, which is less 

 remote than the width of the axis, with patent not recurved spines 

 as long as the portion within the fulcra. The thorax tapers back- 

 ward rather rapidly to the tail, which has a short three-ribbed axis, 

 and the upper pair of its pleurae are very much expanded, widely 

 divergent, and more arched than in our figure, which also represents 

 the thoracic pleura3 as less curved tlian they really are. The hinder 

 portion of the tail is absent on our specimen ; and I know of no other. 



Locality and Geological Position, — Caradoc Rocks of Desert- 

 creat, Tyrone (Mus. Pract. Geology). 



A third form, very abnormal in its characters, and of large size, 

 has been named S. Maclareni by Prof Wyville Thomson, after the 

 veteran Scotch geologist, in whose company he found it. It is, 

 however. Prof Thomson's previously described Acidasjns unica. 

 As he has mislaid his own full description, I may supply the follow- 

 ing notes, from his specimens and others presented to the Museum 

 of Practical Geology by himself 



