OF THE SPECIES. 61 



both of which are relatively longer than in the preceding- species. Caudal shield oblong 

 parabolic, rather pointed, with a broad axis, which reaches to only three fourths of the length 

 of the shield, and consists of nine rings ; the lateral parts furnished with eight radiating 

 furrows. 



Occurs in the blackish-gray clayslate of Angers, in specimens in the Berlin Museum 

 (No. 10. 1). 



Renun-ks. — 1. There is no figiu-e of this species in Gucttard's 'Treatise on the Slate of Angers' 

 (Mem. fie TAcad. de Scieuc., 1757, p. 82), or at the most it is only the figure marked 3, in Table VII, 

 (V), that could be considered as such. 



2. Murchison describes several Tiilobites in his work, which have been taken for Ogtji/ia by other 

 authors,, but which do not belong to this genus. Asajikus corndensis (G63, PI. XXV, Fig. 4) certainly 

 approximates in many respects to O. Buchii, but is probably a genuine Asajj/ius ; at least, this is the 

 case if the lateral lobes of the rings of the body ha\e been con-ectly represented. A. duplicatu.i, 

 (ibid. Fig. 8,) on the other hand, is probably only a flattened caudal shield of Oijijgia Buchii, in its 

 young state. The figui'es of Asaph, tyrannus (G62, PI. 'XXIV and XXV, Fig. 1) do not belong to 

 Ogyyia, but are also to be referred to Asuphus. 



3. Ogygia Desmaresti, Brongn. I. c. 28. 2, PI. Ill, Pig. 1 ; Schlote. Nachtr. 23. 2, and 35. 14 ; 

 Dalm. Palaad. 72. 2; Milne Edw. Crust. 338. 2; Emmr. Dm. 27. 2. The impression of a fragment from 

 the lower side presents too few characters to enable one to found a separate species. The specimen 

 perhaps only belonged to a very large specimen of the Ogygia Buchii, the rings of which are partially 

 pushed one above another, and for this reason appear small. It certainly belongs to Ogygia. 

 Guettard's figures, which are quoted by Milne Edwards, relate to quite a diflereut species, namely, my 



Ilhenus giganteus. 



Division B. 



Trilobites having a simjjle, though tolerabig large caudal shield, the axis of which consists 

 of but few joints, and is always .shorter than the body. 



The genera belonging to this division may be divided, according to the number of 

 body rings, into eight jointed and ten jointed. 



First Subdivision (a). 



Eight-jointed Trilobites with a short articulated caudal a.xis, incapable of rolling them- 

 selves up. — Odontopleurid.e. 



Genus 3. — Odontopleura, Emmr. (Acidaspis, Murch. ; Ceraurus, Locke). 



This remarkable genus is closely allied in habit to the preceding, and is highly interest- 

 ing in a zoological point of view, because the two species are commonly distinguished from 

 one another in the same manner as the species of the preceding genus. 



The cephaHc shield is subsemicircular, the longitudinal radius being much shorter than 

 the other ; the moderately convex glabella is undivided in its length, contracted towards the 

 posterior part, and furnished with a strong articulating varix ; it enlarges laterally, and at 

 this point has three other little knobs beside it in two rows. 



The facial suture resembles that of Ogygia, forming at the anterior part an arcli before 

 the glabella, then extending inwards to the eye ; thence turning to the posterior margin, 

 and penetrating it at about one fourth of the distance from the terminal angle. 



