240 paljeontolooy of new«york. 



Genus ACIDASPIS ( Muhchison ). 

 ODONTOPLEURA (Emmrich). 



I prefer to adopt the name of Muhchison, which is well understood in its application 

 to a species in tlie central or higher Silurian strata of New-York. It is not easy to determine 

 whether the name of Morchison or Emmrich has priority in regard to time ; the works of 

 the former, and the dissertation of the latter, bearing the same date. 



Dr. LovEN (0/r. Vet. Acad. Sci. Stockholm, 1845) has attempted to show the identity of 

 AciDASPis, Odontopleura and CeraurIjs J but the latter genus is quite distinct, as I shall 

 show in the succeeding pages. 



299. 1. ACIDASPIS TRENTONENSIS. 



Pi.. LXIV, Figs. 4 a, b, c, d, e,f. 



Compare Cerattrtu croaotus, Locke in Am. Jour. Science, 1843, Vol. xliv, no. 2, p. 346. 

 Odontopleura ovata, Emmrich, Dissertation, 1S39. 



— bitpinota. Id. Scient. Memoirs, 1843, Vol. iv, part 14, pag. 275, pi. 4, fig. 12. 



Cephalic shield subcrescent-form, broadly rounded and dentated in front, produced into 

 elongated spines at the posterior angle, the connate segment at the base distinct ; glabella 

 of nearly equal width, somewhat straight, and having a projecting spine at the posterior 

 margin, and two distinct rounded lobes or tubercles on each side, or in the furrow between 

 the glabella and cheeks, being nearly disconnected with the former ; cheeks with a lon- 

 gitudinal or slightly oblique groove from the inner posterior base of the eye, extending 

 forward, and a ridge from the front of the eye, extending forward and inward along the 

 facial suture ; outer margin of the maxillee fimbriated ; eyes round smooth tubercles ; 

 body ten-jointed ; lateral lobes with a row of small tubercles on the anterior edge of each 

 articulation ; caudal shield two-jointed, with a spinous margin. 



In our specimen, both the spines from the angles of the buckler, and the one from the 

 posterior part of the glabella, are broken off. That they existed in accordance with other 

 species of the genus, is clear from the appearance of the remaining portion. The extremities 

 of the pleura, or lateral articulations, are prolonged into short spines as in the Odontopleura 

 bisjnnosa of Emmrich cited above, and in the figure of the same species given by Bur- 

 MEiSTER ; but the character of the caudal extremity, and the serratures on the margin of 

 the buckler, as well as the tubercles of the middle lobe of the thorax, as represented by 

 these authors, are different from our specimen. The form of the buckler, the tubercles of 

 the glabella, eyes, etc., clearly point to Jiddaspis of Murchison. We have another ana- 

 logous species in the Delthyris shaly limestone, which resembles the Addaspis brightii of 

 England. 



