30 Xoj'th American Palaeozoic Crustacea. 



Palaeocreusia, Clarke, 1888 ; Pal. New York, vol. 7, p. 210. 



Devonica, Clarke, 1888 ; Pal. New York, vol. 7, p. 210, pi. 36, figs. 24, 26. 



Coniiferous. 

 Prestwichia, Woodward, 1867 ; Quart. Jour. Geol. Soc. London, vol. 23, p. 32. 



A generic name proposed for tlie so-called fossil Limuli, in which the 

 thoracic and abdominal segments are not divided, and in which the 

 former appear to be anchylosed. Type Prestwichia anthrax (Prestwich), 

 Woodward. 



Danse (Meek & Worthen), Packard, 1886 ; Mem. Natl. Acad. Sci., vol. 3, 

 p. 146, pi. 5, figs. 3, 3a; pi. 6, figs, la, 2, 2a. 



For other references to this species see Enproiips and Belinurus. 



Eriensis, Williams, 1885 ; Am. Jour. Sci., 3d series, vol. 30, p. 46, 3 figures. 

 (See Protolimulus Erietisis.) Devonian. 



Protolimulus, Packard, 1866; Mem. Natl. Acad. Sci., vol. 3, p. loO. 



Diiiijnosis. — Cephalothorax relatively large sub-semicircular, genal angles 

 produced. Cephalic appendages small ; terminal segments of the 

 posterior members foliaceous. Abdomen composed of 6 (?) segments, 

 including the large caudal spine. (Hall & Clarke, 1888 ; Pal. New 

 York, vol. 7, p. xlviii.) 



Eriensis (Williams), Packard, 1886 ; Mem. Natl. Acad. Sci., vol. 3, p. 150, 

 figs. 11-13. 



Eriensis, Hall k Clarke, 1888; Pal. New York, vol. 7, p. 153, pi. 26, 

 figs. 1, 2. 

 Primitia, Jones & Roll, 1865 ; Annals & Mag. Nat. Hist., 3d series, London, 

 vol. 16, p. 415. 



Gen. Char. — Carapace minute, bivalved, either equivalved or nearly so, 

 convex, more or less oblong, often approaching Leperditia in shape, by 

 the sloping of the dorsal angles ; hinge-line straight, sometimes nearly 

 as long as the valve. Surface of each valve usually impressed on the 

 dorsal region, eitlier medially or towards the anterior extremity, with 

 a vertical sulcus, variable in size, sometimes barely visible, sometimes 

 passing into, or even merely represented by, a navel-like pit ; and 

 sometimes the sides of the sulcus are swollen and even raised up into 

 tubercles. 



cristata, Whitfield, 1889 ; Bull. Am. Mus. Nat. Hist. New York, vol. 2, 

 p. 59, pi. 13, figs. 1, 2. Calciferous. 



gregaria, Whitfield, 1889 ; Bull. Am. Mus. Nat. Hist. New York, vol. 2, 



p. 58, pi. 13, figs. 3-5. Calciferous. 



Bei/richia Logani, var. leperditioides, Jones, 1858; Annals & Mag. Nat. Hist., 



3d series, London, vol. 1, p. 244, pi. 9, fig. 10. Trenton. 



Beyrichiu Loyani, var. leperditioides, Jones, 1858 ; Geol. Survey Canada, Dec. 3, 



p. 91, pi. 11, figs. 1-5. 



leperditioides, Jones, 1884 ; Annals & Mag. Nat. Hist., 6th series, London, 

 vi.l. 14, p. 345. 

 Beyrichia (Primitia) occidentalis, Walcott, 1884 ; Pal. Eureka Dist., Mon. U. S. 

 Geol. Survey, No. 8, p. 204, pi. 17, figs. 4, 4 a. Devonian. 



