38 ACANTHOCHITES-LOBOPLAX. 



The gills extend forward half-way to the head. 



Length 21, breadth 7* mill, (dry specimen.) 



Length 24, breadth 13 mill, (large alcoholic specimen.) 



Key West and Key Largo, Florida, on the reefs near low tide 

 (Heinphill); Dry Tortugas (Dr. E. Palmer); Cape Florida 

 (Wurdeman.) 



Notoplax floridanus DALL, Bull. Mus. Comp. Zool. xviii, Report on 

 the ' Blake ' Mollusca, p. 416, (1889.) 



This species attracts the attention at once by its dark, glistening 

 girdle, and the long line of white strokes along the median line, like 

 exclamation points without the dots ('). It resembles no known 

 species but A. porosus Burrow, of New Zealand ; but the latter differs 

 in having the dorsal stripes slightly more reduced, and in having a 

 row of projecting pore-hillocks along each side. In floridanus the 

 pores are extremely indistinct even in alcoholic specimens, and in 

 dried examples they can only be detected by looking through the 

 specimen at a strong light. 



One of the specimens before me, collected by Hemphill lacks 

 black pigment in the girdle, being of a light brown tint. It is prob- 

 ably an albino. Dall says that the portion of the tail plate between 

 the (two) notches is not serrate, but in my specimens it is very dis- 

 tinctly slit. The number of pores around the front margin of the 

 head valve is not 5, but 4, as is the rule in Acanthochites and its sub- 

 genera ; this of course does not include the two at the suture. 



Section Loboplax Pilsbry, 1893. 



Phacellopleura CPU. MS., not Phakellopleura Guilding. 



Valves partly covered, the anterior valve having 5 radiating ribs, 

 and the same number of lobes along the margin ; the posterior valve 

 having the insertion-plate grooved outside, notched and slit along the 

 edge, between the usual postero-lateral slits. Girdle leathery, having 

 minute sutural tufts. Gills (of A. molaceus} extending along the 

 posterior two-thirds of the foot. 



In the nakedness of the girdle and the form of the individual 

 valves, as well as the strong denticulation of the posterior valve, 

 this group recalls Katharina ; but in that genus there are no sutural 

 girdle-pores or tufts whatever, and the tail valve is quite distinctly 

 sinused behind. Loboplax differs from Notoplax in the lobed and 

 ribbed head valve, the more distinct posterior slits, and more naked 

 girdle. 



