OF THE SPECIES. 59 



Genus 2. — Ogygia, Brongn. 



Cephalic shield semicircular or parabolic, flat ; the glabella moderately convex, con- 

 tracted towards the posterior part, with three slight lateral impressions; cheek -shields 

 lengthened into a more or less extended posterior angle. 



Eyes moderately arched, semicircular, affixed centrally beside the glabella. 



Facial suture very distinct, running in an arch towards the left and right, parallel with 

 the anterior margin, between the latter and the glabella; then turning almost at a right 

 angle towards the eye, forming the well-known plate above it ; and then with a curve in the 

 shape of the letter Sj turning towards it parallel to the posterior margin in the principal 

 direction, and terminating there at about three fifths of its extent from the glabella. 



Body certainly composed of eight joints,* the joints short, but tolerably broad, yet 

 less by one half than the lateral lobes ; the latter straight, flat, bent strongly backwards at 

 their extremities, and pointed. 



Caudal shield corresponding with the cephalic shield, its axis as long as the body, 

 many-jointed, its sides furnished with radiating furrows, the interstices of which are again 

 divided by smaller half rays. 



Locality. — In the oldest fossiliferous rocks. 



Remark. — This genus stands in so remarkable a degree of affinity to the preceding, that the 

 circumstance of its hitherto hanng frequentl}' been confounded with the perfectly heterogeneous species 

 of Asaplms is truly surprising. It is elf ar that even acciu-ate observers, as Emmerich and Boeck, have 

 not always estimated correctly tlie zoological position of these fossils. 



1. O. Buchii : Scuto capitis caudasque semicLrculato ; iUius angulis posticis acuminatis. Long. 

 3-5". Table 1, Fig. 2. 



Lhwyd, Phil. Tr. vol. xx, 279, tab. add. Fig. 15. Iclm. Brit. Ep. i, Table XXII, Fig. 4, 



{see Brunn.) Tril. dilatatus, Brunn, Kjobeuh. Wiclcnsk. Selsk. Sriff. 1781, i, 



393, IV. Parkinson, 0/y. Bern, etc., iii, PI. XVII, Figs. 13, 15 (?). As. d. Dalm. 



Palcead. 67. 8, Tab. Ill, Fig. 1. Emmr. Diss. 28. 5. Sars, Ms, 1835, 336, Table 



VIII, Fig. 5. Isot. dilat. Milne Edw'ards, Crm. iii, 302. 9. Ascqi/i. de Buchii 



Brongn. Cr. f. 20. 2, Plate II, Fig. 2, A, B, C. Schloth. Nachtr. ii, 34. 8. 



Dalm. Palcead. 68. 9. Murch. Sil. Syst. ii, 662, Plate XXV, Figs. 2, 3 (young). 



Emmr. Diss. 28. 5. Milne Edw. Crust, iii, 309. 5. 



Cephalic shield nearly semicircular, but the longitudinal radius a little shorter than the 



transverse, furnished at each side with three slight transverse impressions, by which two 



anterior smaller lateral lobes, and a third posterior broader lateral lobe are indistinctly 



bounded ; the posterior margin is rather distinctl}^ turned up. 



Eyes not large, semicircular, corresponding in their position to the two anterior smaller 

 lobes of the glabella. Cheek-shield with a concentric canal-like groove towards the exterior 

 margin, and wdth a strongly prominent posterior angle, which in smaller specimens reaches 



* Quenstedt defends the se\ cn-jointcd figures, which were represented from defective specimens ; 

 but all the well-preserved specimens that I have seen have had eight rings. 



