BRITISH FOSSILS. 



Decade VII. Plate III. 



SPILSREXOCHUS HIBUS. 



[Genus SPH^REXOCHUS. Beteich. (Sub-kingdom Articulata. Class Crustacea. 

 Order Entomostraca. Tribe Trilobitss or Palsedae.) Eyes facetted ? " Head Tery convex, 

 the cheelcs not scrobiculate ; facial suture ending on the external margin near the angles, 

 in front continuous and submarginal; glabella large and nearly spherical, with three 

 furrows on each side, the two upper very obscure, the lower strong and curved down to 

 the neck furrow; thorax of 11 joints, without any furrows ; tail of 3 segments, free 

 at their ends ; " hypostome subtrigonal, with a marginal furrow, but without lateral 

 furrows. No rostral shield.] 



Diagnosis. S. granulosus ; glabelld lobis infimis profunde circum- 

 cinctiSf paullum tumidiSy — spatio inter jecto diametrum eorum super ante ; 

 caudd pleuris tumidis^^ 



Synonyms. Calymene clamfrons^ Hisinger(1840), Leth. Suec, Supp. 2d. 

 t. 37. fig. 1 (not of Dalman.) Sphcerexochus mirus, Betrich (1845), iiber 

 einige Bohm. Tril., p. 21. S. mirus, ibid., Zweite Stiick(1846), 1. 1. fig. 8. 

 S. calvuSy 'WCoY (1846), Syn. Sil. Foss. Ireland, pi. 4. fig. 10. S. mirus, 

 CoEDA (1847), Prodrom. einer Monog. Bohm. Tril., fig. 72. Barrande 

 1^1853), Syst. Sil. de BoMme, vol. i. pi. 42. fig. 11-18. 



We are indebted to Mr. John Gray for the fine Dudley specimens 

 which figure in this plate, and to Mr. Fletcher for those from which 

 the details are drawn. Fragments and detached heads are not 

 uncommon ; but these are the only perfect British specimens we 

 are acquainted with. The species is cosmopolitan, at least it ranges 

 from Bohemia to the Western States of America, and in our own 

 country is found both in Upper and Lower Silurian rocks. 



Description. — The animal is capable of rolling itself into a com- 

 plete ball, of which the large head forms a very conspicuous part. 

 The general form is oblong ; the length of English specimens usually 

 about an inch, and a half, and the breadth ten lines ; they never 

 appear to reach the length of two inches. 



The head is more than one third the whole length, and the glabella 

 is very large, occupying, as seen from above, four fifths of the width, 

 [VII. iii.] 7 c 



