CERATIOCARTS. i) 



In describing the parts in the fossil forms, we have to deal with — 



1. The two valves of the carapace, and the rostrum in front between them 

 (rarely present). Their ventral rim, raised, and occasionally pitted with the bases 

 of lost set(e or pricJcles. Their superficial ornament. In some allied forms tubercles 

 or nodes are present, one of which may be distinguished as an optic tubercle or eye- 

 spot ; while others are due to the maxilla; (teeth), or other mouth-organs, or to 

 places of attachment for the buccal muscles of the masticatory apparatus. The 

 cephalic region of the valve is sometimes marked off from the thoracic by a slight 

 sulcus (the nuchal furrow ?). 



2. The somites or abdominal segments vary in number ; some are covered by 

 the carapace, others exposed. Their articulation ; superficial ornament ; occasional 

 prickles ; their appendages {uropods) rare ; and terminal spines. The ultimate 

 segment has its own special characteristics. 



3. The caudal appendages or spines, consisting of a median telson} [urosome) or 

 style, and two smaller lateral stylets or cercopods. Their ridges and furrows, and 

 pits, indicating bases of little spines or spinules, former setae, fringes, or fimbrio. 

 The proximal end of the telson has often its special ornamentation. 



Genus Ceeatiocaeis, M'Coy, 1849. 

 1839. Onchus, Agassiz (in part). In Murchison's ' Silurian System,' p. 607. 



1848. — Phillips (in part). ' Mem. Geol. Surv.,' vol. ii. Part 1, p. 226. 



1849. Pterygotus, M'Coy. 'Ann. Mag. Nat. Hist.,' ser. 2, vol. iv, p. 394. 

 1849. Geratiocaris, M'Coy. ' Ann. Mag. Nat. Hist.,' ser. 2, vol. iv, p, 412. 

 1851. Geratiocaris, M'Coy. ' Brit. Palasoz. Fossils,' Fasc. 1, p. 136. 

 1851. Pterygotus, M'Coy. 'Brit. Pateoz. Fossils,' Fasc. 1, p. 175. 



1851. Leptocheles, M'Coy. ' Brit. Palfeoz. Fossils,' Fasc. 1, p. 176. 



1851. Pterygotus (Leptocheles), Bronn. ' Lethsea Geognost.,' vol. i, Part 



1, p. 40. 



1852. Onchus, James Hall. ' Geol. Surv. New York, Palaeontology,' vol. ii, 



p. 320. 



1852. Geratiocaris, Bronn. ' Lethgea Geogn.,' vol. i. Part 2, p. 539. 



1853. Bithyrocaris, Geinitz. ' Verst. Grauwack. Sachsen,' Heft ii, p. 23. 

 1853. Leptoclieles, M'Coy. ' Quart. Journ. Geol. Soc.,' vol. ix, p. 13. 



1853. Geratiocaris (Leptocheles) , Barrande. 'Neues Jahrb. fiir Min.,' &c., 



1853, Heft iii, p. 342. 



1853. Bithyrocaris ?, D. Sharpe. ' Quart. Journ. Geol. Soc.,' vol. ix, p. 158. 



1854. Geratiocaris et Leptocheles, Murchison. ' Siluria,' 1st. edit., p. 236. 

 1854. Geratiocaris, Morris, ' Catal. Brit. Foss.,' 2nd edit., p. 102. 

 1856. — Salter. ' Quart. Journ. Geol. Soc.,' vol xii, p. 33. 



1 This is really the last joint (somite) of the abdomen. 



