60 SYSTEMATIC ARRANGEMENT 



to the third, in larger to the sixth abdominal ring. Body distinctly furnished with eight 

 joints, sometimes owing to the dislocation of two successive rings appearing to be limited to 

 seven (see Remark 2); the rings narrower than the half-lateral lobes, moderately arched; the 

 lateral lobes quite flat, at the end arcuated, curved towards the posterior part, with a strong 

 diagonal furrow, which, however, does not quite reach to the terminating angle. Caudal 

 shield formed like the cephalic shield, but its longitudinal radius larger than the transverse, 

 therefore approximating to the parabolic form ; the axis gradually reduced towards the 

 posterior part, rounded off at the end, distinctly articulated, the number of rings in it 

 different according to age (usually thirteen), with a rather longer terminal joint ; in younger 

 specimens the number is eleven, in older ones as many as seventeen ; the rays beside the 

 axis on the shield usually fewer by about two than the number of joints of the axis ; thus, 

 for example, when the number of joints is thirteen, exhibiting eleven rays, with slight traces 

 of a twelfth, besides the two end joints, which are also indistinctly separated ; the intervals 

 between the rays again divided by an oblique diagonal furrow, similar to the lateral lobes 

 of the rings of the body. 



Remarks. — 1. Asaph, dilatatus and A. de Buchii of authors are probably the same species. The 

 figure in Dalman's work is drawn from a cast, and owing to tins cii-cumstance is very indistinct, so 

 that I have preferred the latter name, the species having been fii-st represented distinctly under that. 

 Parkinson's, Brougniart's, and ^Nlurchison's distinct figures leave no doubt as to the identity of the 

 species. Lliwyd's figure in the ' Philosophical Transactions' also represents this species tolerably well, for 

 which reason it has been quoted by Brunnich from the ' Ichnographia Britaunica.' Individuals vary 

 very much in point of size ; I have a caudal shield before me from the collection at Halle (No. 639), 

 wliich is scarcely so large as a sixpence, having eleven joints in the axis, a pretty long undinded 

 terminal joint, and ten rays. The number increases by the progressive division of this longer terminal 

 joint with increasing age. Another specimen of the same rock (a blackish-gray grauwacke, locality 

 unknown) was figured by me, and compared with perfect specimens in the Berlin Museum (Nos. 9.8 

 and 9). 



2. Quenstedt adheres to the view that these Trilobites are seven-jointed, and founds his opinion 

 on the figiu-es given by Dalman and Brongniart (3, A), as well as on original specimens. There are 

 certainly two well-preserved fragments in the Museum at Berlin (Nos. 9.1, and 9.5), with only seven 

 distinct joints ; but there are also others, equally distinct, with eight joints (Nos. 9.8, and 9.9) ; and the 

 former number can therefore only be owing to a dislocation of two rings one under another. Con- 

 sidering that the impressions arc merely those of shells, such a dislocation is very conceivable, and the 

 more readily so, the less perfectly the shell had been preserved. The same remarks hold good with regard 

 to the other species. 



2. O. Guettardi: Scuto capitis caud;cque parabolico ; illius augulis posticis longissime acuminatis. 

 Long. 3-6 inch, Table I, Fig. 3. 



Brogn. Cr.fo.'^s. 28. 1, Plate III, Fig. 1, A,B. Bronn, Leth. 1. 119, Table IX, Fig. 19. 



BucKLAND,Ä%. Tr. Plate XLVI, Fig. 9. Milne Edw. Crust. iii,337. 1. Dalm. 



Palaad. 72. I. Emmr. Diss. 27. 1. Tril. Gaett. Schloth. Petrf. Nacldr. ii, 93, 



and 35. 13. 0(iy(iia MurcMsoni, Murch. Sil Si/st. 664, Plate XXV, Fig. 3, a (the 



lower figure h does not belong to Of///f/ia, but to an Jsajj/ii/s). Milne Edw. /. c 



338. 3. 



Cephalic shield olilong parabolic, rather pointed ; the glabella, as far as it can be 



recognized, formed as in the preceding species ; the eyes oblong elliptical ; the posterior 



angles of the cheek-shield as long as all the rings of the body together, or even longer. 



Eight body rings, their transverse diameter larger than half the breadth of the lateral lobes. 



