192 BRITISH PALEOZOIC PHYLLOCARIDA. 



21. Dithyrocaris Kayseri, /. M. Olarke, 1884. ' Neues Jahrb. f. Min.,' &c, 



1884, p. 185, pi. iv, fig. 6. 



This, one of the largest sets of tail-spines known for the genus, is much 

 crushed and imperfect. The best-preserved stylet measures at least 50 mm. in 

 length, and is 12 mm. wide near its top. The style was very much larger and 

 longer (the fragment is 100 mm. long, and nearly 20 mm. wide at top, and 7 

 mm. wide at its broken end. All three spines are uniformly convex, tapering to 

 sharp ends, and are delicately striate longitudinally. 



From the Upper Devonian of Wildungen, Germany. 



Mesothyra. — Some very large forms of an allied genus, from the Devonian 

 strata of North America, must be here referred to. The genus Mesothyra differs 

 from Dithyrocaris especially in having a narrow plate along the hinge-area between 

 the dorsal edges of the two valves. 



1. Mesothyra Neptuni, Hall, 18(53. 



Dithtrocaeis neptuni, Hall, 1863. Sixteenth Annual Report of the New York 



State Cab. of Nat. Hist., Appendix D, 

 p. 75, pi. i, fig. 9. 



— — 1876. Palaeontology of New York, vol. v, part 2 



Illustrations of Devonian Fossils (published in 

 advance of the Pal. New York), pi. xxiii, fig. 6. 



— Miller, 1877. Amer. Pal. Foss., p. 217. 



— Packard, 1883. Monogr. N.-Amer. Phyllop. ; Twelfth 



Ann. Report U.S. Geol. Surv., p. 452, fig. 73. 



— E., W., and J., 1888. Rep. Brit. Assoc, for 1887, p. 65. 

 Mesothyra neptuni, Hall and Clarke, 1888. Palaeont. New York, vol. vii, with 



Supplement to vol. v, part 2, p. 191, pi. xxxii, 

 fig. 7 ; and pi. xxxiii, fig. 1. 



— Miller, 1889. North American Geol. and Pakeont., p. 556. 



— Vorjdcs, 1893. Bibliogr. Pal. Crust., p. 299. 



— Clarke, 1893. American Naturalist, Sept. 1st, 1893, p. 796. 



^Caudal plate (27 mm. wide) ami telson [style] 81 mm. loug. 

 I Cercopods [stylets] 110 mm. long. 

 Size <j Style (from its joint in the caudal plate) 75 mm. Ion 



and 15 mm. wide at top. [As figured. 



^-Stylets 120 mm. long, and 15 mm. wide at top. 



