MAKYLAXD GEOLOGICAL SURVEY 431 



Amphidetus orthonotus Conrad, 1846, Am. Jour. Sci., ser. ii, voL i, p. 330. 

 Amphicletus orthonotus McCrady, 185.5, in Pleiocene Fossils of South Carolina, pp. 



6, 7, pi. ii, tis?s. 1, la, lb, Ic. 

 Echinocardium vircjirdanum Desor, 1858, Syn. des Echinides Fossiles, p. 408. 

 Amphidetus virfjinianHs Emmons, 1858, Kept. N. Car. Geol. Survey, p. 310, lig. 



345 a, b, c. 

 Echinocardium orthonotus Conrad, 1865, Proc. Acad. Nat. Sci. Phila., p. 75. 

 Echinocardium pennatifidnm (?) A. Agassiz, 1873-1874, Revision of Echini, Cat. Mus. 



Comp. Zool., No. vii, pp. Ill, 351. 

 Amphidetus virgiuianus Schliiter, 1899, Zeit. d. Deutsch. geol. Gesell., Bd. Ii, p. 113. 



Description. — " Ovate, convex-dej)resse(l ; truncated at each end, more 

 elevated anteriorly than posteriorly; dorsal line of the suture a little ele- 

 vated, and curved gradually to the mouth of the anterior half; on the 

 posterior, straight to the margin and parallel to the hase ; canal very wide 

 and slightly impressed on the back, margined by an obtuse carinated line 

 and slight furrow ; on the periphery the canal is deep and angular ; am- 

 bulacra rapidly expanding from the extremities toward the dorsal suture ; 

 pores disunited; in the middle of the back a slight furrow crosses ob- 

 liquely each of the anterior ambulacra at its termination ; base plano-con- 

 vex; anus large and remote from the margin; granulations on the back 

 minute and very closely arranged, in the canal much larger and unequal 

 111 size; base with large tubercles, becoming gradually smaller and more 

 closely arranged towards the margins. Length, two inches and three- 

 eighths; diameter, two inches and an eighth; height, one inch and an 

 eighth." Conrad, 1843. 



The " slight furrows " crossing the " anterior ambulacra " and the 

 " slight furrow at the margin of the wide and slightly impressed canal " 

 were probably parts of the shield shaped internal fasciole characteristic of 

 the species. 



" Body broadly ovate ; elevated and truncate posteriorly. Back oblique ; 

 dorsal impression lanceolate-scutate, are a very slightly excavated ; ambu- 

 lacral spaces broad, triangular, depressed ; interambulacral spaces slightly 

 convex. Anteal furrow broad, shallow; sides slightly gibbous; subanal 

 impression broadly obcordate; postoral spinous space broadly lanceolate. 



" Dimensions of the smaller but more perfect specimen : Lon., unc. 

 1 11-12; lat., 1 8-12; alt., 1. Xumber of pairs of ambulacral pores :^ 



'In another specimen the number was found to be Ant. lat. dors. amb. 8 + 13. 

 Post. lat. dors. amb. 11 +11. And four pairs additional on each side of the ovarian 

 holes. 



