DESCRIPTION OF THE PLATES. 131 



Fig. 2. c. Rolled up, side view. 



Eemark. — Particular attention has been paid to the sculpture in both figures, 

 and the body has therefore been represented only in outhne. 



3. Arcliegonus claviceps. 



4. Caudal shield of Asaphws Tijrannus. 



5. Aeonia Slokesii, cephalic shield. 



6. ^/^»o.y/«« jöM{/bn«/s, cephahc shield. 



7. The same, caudal shield. 



8. Aeonia concinna. 



9. Aeonia verticalis, Gerastos cornutus, Goldf. 

 10. Pkacojjs Ilaiismanni. 



Remark. — Two forms of the caudal shield of this species occur in the grau- 

 wacke hmestone of Bohemia, of which the one, which is the rarer species, 

 is more elongated, and has 21 joints of the axis, upon which two larger 

 tubercles are placed near the centre. The lateral lobes, 1 5 in number, are 

 broader, more depressed at the upper part, less distinctly impressed longi- 

 tudinally, and the granulation of the siu-face is more scattered. The 

 other form (represented here) is shorter, broader, and more obtuse; has 

 only from IS to 19 rings in the axis, and 13 more convex and narrower 

 lateral ribs, which are distinctly furrowed at the angle, and very finely, 

 and, on the axis, uniformly granulated. I suspect that the former form 

 may have been the male, the latter the female individual. 



TABLE VI. 



Fig. 1. AjMS cancriformis, viewed from below, natural size, very old. 



2. Serolis paradoxa, from above, fuU grown. 



3. Brancldpus stagnalis, from below, enlarged to six times its diameter. 



4. Structure of the eyes oi BrancMjMs. 



a. Cornea extern, laivis. 



b. Cornea ai-eolata. 



c. Lens. 



d. Corpus vitreum. 



e. Commencement of the black pigment. 

 /. Nervus opticus. 



5. Parts of the mouth of Avus. 



A. The jaw. 



B. 1 P. The accessory parts of the mouth. 



C. 2 P. Do. do. 



D. Rudiment of the first foot. 



6. Parts of the mouth of Brancldpus. 



A. The jaw. 



D. Rudiment of the fijrst foot. 



