PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 315 



Microplax H. Adams. 



Resembling Chitonellua externally; submerged laminae unslit, entire, fused in an 

 undistinguishable manner •with the parts which usually constitute the sutural 

 laniinse. M. Grayi Ad. & Aug. 



The paleozoic Helminthochiton Salter, Priscocliiton Billings, Grypho- 

 chiton Gray, and several unpublished names of Dr. Carpenter, all belong 

 to the Leptoidea. A large number of the fossils described as Chitons 

 (for instance Sulcochiton Grayi Byekholt) are not niollusks; many of 

 them being valves of Balani or fragments of isopod crustaceans. 

 Leptochiton cancellatus. 



Chiton cancellatus Sowerby (as ? of Leach MS.), Conch. 111. f. 104-5, 18,39. 



Chiton albus Pulteney, non Lin. fide Hanley. 



Chiton cancellatus Reeve, Conch. Ic. pi. lix, f. 152, 1847. 



Chiton asellus Midd. Mai. Ross, i, p. 122, 1847, not of Lowe. 



Chiton cancellatus Forbes & Hanley, Brit. Moll, ii, p. 410, pi. lix, f. 3, 1853 



(outlines inverted in figure). 

 Leptochiton cancellatus H. &. A. Adams, Gen. Rec. Moll, i, p. 473, 1854. 

 Chiton cancellatus Jeffreys, Brit. Conch, iii, p. 217, 1865; v, p. 198, pi. lvi, f. 1, 



1869. 



Chiton alveolus Jeffreys, 1. c. iii, p. 218, 1865; not of Sars. 

 Chiton Bissoi auct. not of Payraudeau. 



Lepidopleurus cancellatus Sars, Moll. Reg. Arc. Norv. p. Ill, t. 7, f. 6 a-h, 1878, 



dentition t. I. f. 8, (imperfect). 

 f Lepi(lopleuru8 arcticus Sars, 1. c. p. 112, t. 7, f. 7 a-h. 



f = Chiton islandicus Gmelin, S. N. 3206, 1788.— Schroter, Einl. iii, p. 509.— 

 Dillwyn, Rec. Shells, i, p. 10, 1817. 



L. t. minima, elongata, valde elevata, regulariter arcuata; jugo nullo; 

 aurantia plus minusve cinereo tincta, interdum albida ; valvis angus- 

 tioribus, hand rectangulatis, apicibus nullis; mucrone centrali, valde 

 elevato, sculp tura ut in L. asello, sed granulis parura majoribus ; areis 

 centr. parum divergentibus, areis lat. satis definitis, vix elevatis; intus, 

 laminis sut. minimis, triangulares; sinu latissimo, marginibusque 

 valvarum a sculptura externa paullulum crenulatis; zona, angusta, 

 squamuliis tenuibus, haud imbricatis, haud striulatis, dense obsitu. 

 Lon. 6, Lat. 3 mm. Div. 80°. 



Hob. — British seas; Norwegian coast in 50-100 fms.; Greenland; 

 Gulf of Lyons (Jeffr.); Lofoten, 300 fms. (Sars); Vigo, Spain (McAn- 

 drew); Dalmatia (Brusina); Alaska, at TJnalashka, Shumagins, Port 

 Etches, and Sitka Harbor, 6-100 fms. Dall ! Ninety-four specimens ex- 

 amined. 



This species without careful inspection will usually be confounded 

 with small specimens of Trachydermon albus, but a glance at the sculp- 

 ture is sufficient to separate it. From several other species of Leptochi- 

 ton it is less readily distinguished, and a magnifier is indispensable. 

 The differential characters are as follows: 



The pustules which constitute most of the sculpture are arranged 

 like overlapping coins or a solid-linked chain in lines which in the dor- 



