416 BULLETIN OF THE 



sanguineus Reeve is a mere color variety of limaciformis, but has generally 

 been referred to as a synonym of C. purpurascens C. B. Adams, which from 

 authentic specimens is a totally distinct species from limaciformis. 



Of the Lophyridce and Acanthopleuridce there are no representatives in the 

 Blake Collection. 



Super-Family OPSICHITONIA. 



This group contains those forms in which the anterior and posterior valves 

 are differently articulated, and the posterior plate is usually abnormal, or with 

 a slit or sinus behind. It comprises, for the present, the Schizochitonidce, 

 Placophoridce, Mopaliidce, Amiculidce, and Cn/ptoplacidce^ corresponding to 

 divisions E to I of the paper on the Genera of Chitons previously alluded to. 

 No lossil forms are known, previous to the Pliocene, for this division of the 

 Chitonacea. 



Family MOPALIID^. 

 Genus NOTOPLAX H. Adams. 



Notoplax Adams, P. Z. S. 1861, p. 403. Type, N. speciosa Ad. (Tasmania). 



Notoplax floridanus n. s. 



Surface of valves entirely covered except a small rounded point at the mucro 

 of the anterior valve and a linear space extending forward from the mucro of 

 the others. The exposed parts are whitish and smooth, or transversely finely 

 striate. They are more conspicuous in dry than in fresh or spirit specimens. 

 The exposed part occupies just about the space which the median suture does 

 in the valves of Schizoplax. The covered parts of the valves are whitish 

 clouded with pink. The valves as a whole are wider than long, rectangular, 

 with a very shallow and narrow sinus, except the anterior one are keeled in 

 the median line, overlap each other about half their length, and the two 

 central ones are a little narrower than the others. The valves have about one 

 third the total width of the fresh animal, but about half in the dry specimens. 

 The anterior valve has five notches, the others two each. The mucro of the tail 

 valve is not very prominent, but a little way behind it the immersed portion 

 falls abruptly so that the posterior slope is nearly vertical and the form blunt 

 and high. The part of the tail plate between the notches is not serrate as in 

 N. speciosa, but slightly radiately striate, and the sinus is very narrow, shallow, 

 and almost obsolete. 



The girdle resembles that of Katharina when fresh, being smooth, of a 



black or brown color with the texture of a moist prune above ; below whitish, 



fleshy, a border of extremely minute spines at the margin. When dry there 



is a granular irregularity to the surface, as if there were little irregular grains 



in the substance of the girdle. There are five very small pores about the 

 May 14, 1889. 



