1894.] NATURAL SCIENCES OF PHILADELPHIA. 79 



Posterior valve small, having the mucro obtuse and posterior, the 

 ])Osterior slope short, vertical. 



Interior green, marked with black in the cavity. Head valve 

 having the insertion- plate about one- third as long as the front slope 

 of the tegmentum, with 5 small slits. Intermediate valves having 

 vtrv oblique plates witli 1-1 minute posterior slits; posterior valve 

 having the insertion plate short, and strongly directed forward, with 

 a small slit on each side. Sutural laminae rather lony- and narrow, 

 l)rojecting far forward. Sinus wide, deep and square. 



Girdle microscopically chat!}', with a series of hyaline spicules 

 at the edge and 18 small and compact silvery tufts. 



Length 92, width oJ mm. (dry specimen). 



" 12, "6 " (average specimen preserved in alcohol). 



Abundant in Port Jackson, near S3fdney (Dr. J. C. Cox!). 



This is a very distinct and easily recognized little species, of which 

 Dr. Cox has collected great numbers. It varies interminabh- in the 

 color and pattern of the valves, but not much in sculpture. The 

 subgenus which I have constituted for the reception of this one species 

 may be defined as follows : 



Meturoplux, n. subg. of Acauthochites. Subg. Char.: Valves i to 

 vii as in Acanthochites, but dorsal areas indistinctly differen- 

 tiated; valve viii Jiaving the mucro posterior, tJte iiisertioii-plate stro7i(/li/ 

 directed Jorward, with one slit on each side, and no sinus behind. 

 Girdle as in Acanthochites. Type A. retrojectus. 



This group holds the same relation to Acanthochites that Pallochi- 

 ton holds to Chcetopleura. It is a variation distinctly in the direction 

 of the Cryptojdacidcv, recalling Choneplax, and clearly showing the 

 Acanthochitoid genesis of that family. 



Acanthochites {s. str.) asbestoides Cpr. PI. Ill, figs. 10, 17, 18, 19, 20. 

 -Man. of Conch. XV. p. 17. 



The prominent features of this species are (1), that the dorsal ar- 

 eas are hardly differentiated, being only somewhat smoother than the 

 den.sely granulated latero-pleural areas, and totally lack longitudinal 

 striation. (2) The posterior margins of the median valves are pro- 

 duced far backward in the middle, each strongly imbricating over 

 the following valve, and inside the beak-margin is very broadly re- 

 flexed (fig. 16). (3) The tail valve is disproportionately small 

 (compare fig. 20 with fig. 17) and its sutural-laminae are very long. 



