TRO. — ZAC] 



ARACHNIDA. 



569 



Fig. 1063.— Trinu- 

 cleusconcentri- 

 cus. 



convex ; side lobes wide, flat, straight, 

 pleural groove not reaching the margin ; 

 pygidium subtriangular, margin de- 

 flected, axis conical, about six furrows ; 

 side lobes flat, with about the same 

 number of furrows. Type T. concen- 

 tricus. 



bellulus, Ulrich, 1878, 

 Jour. Cin. Soc. Nat. 

 Hist., vol. 1, p. 99. The 

 young of T. concentri- 

 cus. 

 concentricus, Eaton, 1832, 

 ( Nuttainia concentrica, ) 

 Geo. Text-Hook, p. 128, 

 and Pal. N. Y., vol. 1, 

 p. 249, Trenton to Hud. 

 Riv. Gr. 



Tkopidocaris, Beecher, 1884, Geo. Sur. Pa., 

 vol. PPP, p. 15. [Ety. tropis, a keel ; 

 karis, a shrimp.] Carapace bivalve, 

 semiovate or semielliptical, obliquely 

 truncated behind ; valves about twice 

 as long as wide, having one or more 

 longitudinal ridges ; cephalic region 

 indicated by elevations at the anterior 

 end ; optic node situate on a ridge ; 

 two segments of the abdomen. Type 

 T. bicarinata. 

 alternata, Beecher, 1884, Geo. Sur. Pa., 



vol. PPP, p. 19, Waverly Gr. 

 bicarinata, Beecher, 1884, Geo. Sur. Pa., 



vol. PPP, p. 16, Chemung Gr. 

 interrupta, Beecher, 1884, Geo. Sur. Pa., 

 vol. PPP, p. 18, Chemung Gr. 



Turrilepas, Woodward, 1865, Quar. Jour. 

 Geol. Soc, vol. 21, p. 486. [Ety. turris, 

 tower; Upas, scale.] Elongate, cone- 

 shaped bodies, composed of from 4 to 

 6 vertical ranges of scale-like, subtri- 

 angular plates covered with elevated 

 concentric lines ; plates of middle 

 range convex and bearing a median 

 carina. Type T. wrightana. 



cancellatus, Hall, 1888, Pal. N. Y., vol. 7, 

 p. 216, Up. Held. Gr. 



devonicus, Clarke, 1882, (Plumulites de- 

 vonicus,) Am. Jour. Sci., 3d ser., vol. 

 24, p. 55, Ham. Gr. 



flexuosus, Hall, 1888, Pal. N. Y., vol. 7, 

 p. 215, Up. Held. Gr. 



foliatus, Hall, 1888, Pal. N. Y., vol. 7, p. 

 218, Ham. Gr. 



gracillimus, Ringueberg, 1888, (Plumu- 

 lites gracillimus,) Proc. Acad. Nat. Sci. 

 Phil., p. 136, Niagara Gr. 



newberryi, Whitfield, 1882, (Plumulites 

 newberryi,) Ann. N. Y. Acad. Sci., vol. 

 2, p. 217, Portage Gr. 



nitidulus, Hall, 1888, Pal. N. Y., vol. 7, p. 



218, Ham. Gr. 



squama, Hall, 1888, Pal. N. Y., vol. 7, p. 



217, Ham. Gr. 

 tener, Hall, 1888, Pal. N. Y., vol. 7, p. 



219, Ham. Gr. 



Zacanthoides, Walcott, 1888, Am. Jour. 

 Sci., 3d ser., vol. 36, p. 165. Proposed 

 to receive Olenoides lsevis, 0. spino- 

 sus, O. flagricaudatus, and O. typicalis, 

 but not defined. 



— •o^o» 



CLASS ARACHNIDA. 



The animals, forming the class Arachnida, include the spiders, scorpions, and 

 many offensive parasites and microscopic forms. They are generally possessed of 

 four pairs of legs attached to the anterior division of the body, but have no an- 

 tennae. The Palseozic fossils are nearly all referred to an extinct order, Anthraco- 

 marti, but a few are referred to the living orders, Pedipalpi and Scorpiones. The 

 Pedipalpi have arm-like prehensile organs, terminating in a movable claw, annu- 

 lated abdomen, and long flexible limbs. They inhabit tropical countries, and have 

 a forbidding aspect. The Scorpiones have large palpi or arm-like prehensile organs, 

 terminated by a pair of nippers, and an elongated, tail-like abdomen, which ends in 

 a sharp claw ; and when the animal is in motion, this is carried over the back in a 

 threatening manner. The poison glands are situated at the base of the claw, and 

 when the animal stings, a portion of the venom is thrown into the wound. The 

 scorpions are inhabitants of tropical countries. The Order Anthracomarti is defined 

 as follows : Body more or less depressed ; cephalothorax and abdomen distinctly 

 separable ; cephalothorax frequently made up in large part of pedigerous segments, 



