TRENTON LIMESTONE. 
237 
297. 1. CALYMENE BECKII. 
Pl. LXIV. Figs. 2 a, b, c, d, e. 
Brongniartia carcinoidca. Eaton, 1832, Geol. Text-Book. 
Triarthrus Beckii. Monthly Journal of Geology, 1832, p. 5G0. 
— — Green, 1832, Monograph, pag. 87, fig. 6 (cast no. 34). 
— — Harlan, 1835, Trans. Geol. Soc. Pennsylvania, Vol. i, p. 105. 
— — Id. 1840, Med. and Phys. Researches. 
Paradoxides Beckii, and P. Eatoni. Hall in Am. Jour. Science, 1838, Vol. xxxiii, p. 137. 
Jit ops trilineatus. Emmons, Taconic System, 1844, p. 20, figs. 1, 2. 
— — Id. Agr. Rep. New-York, 1846, pag. 64, figs. 1, 2. (See PI. lxvii of this volume.) 
General form an elongated ellipse, with the posterior extremity narrower, and the sides 
often straight; buckler broadly semioval, the posterior angles rounded ; glabella of equal 
width from base to front, rounded before, deeply trilobate on each side, with a prominent 
thoracic ring at the base; frontal lobe narrowed longitudinally; thorax Avith thirteen 
segments, those of the central lobe with a short spine or tubercle upon the back, those of 
the lateral lobes deeply grooved along the centre ; caudal shield with six or seven segments 
in the middle lobe, and five in the lateral lobes ; posterior extremity obtuse. 
This fossil is of rare occurrence in the Trenton limestone ; but since it has been found 
in this rock, I have given it among the other forms associated in the same position. In the 
compact limestone it presents a very symmetrical form, and is usually more perfectly 
preserved than in the Utica slate, where it is more abundant. 
Fig. 2 a. An imperfect specimen, preserving the thorax and caudal shield, and the left maxillary portion 
of the buckler. 
Fig. 2 b. A perfect specimen, with the exception of the maxillary portions, which are separated at the 
facial suture. 
Fig. 2 c. A similar specimen, preserving the maxillary parts, which give a different outline to the 
cephalic shield. 
Fig. 2 d. Part of a single articulation enlarged, showing the spine upon the centre, with papillose surface. 
Fig. 2 e. A portion of the surface of the buckler enlarged, showing the papillose character of the surface. 
For further illustrations, see Trilobites of the Utica slate, Plate LXVI. 
Position and locality. This species is found in the Trenton limestone at Middleville and 
other places, but is rare in this position. It is one of the most abundant and characteristic 
fossils of the Utica slate, and is more rarely found in the shales of the Hudson-river group. 
It occurs in several western localities, being common in the soft shales of the Blue lime¬ 
stone formation at Cincinnati and elsewhere. {State Collection.) 
