PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 315 



Microplax H. Adams. 



KesembliDg Chitonellus externally ; submerged lamina} unslit, entire, fused in an 

 undistinguisliable manner witli tlie parts whicli usually constitute the sutural 

 lamina?. M. Grayi Ad. Sc Ang. 



The paleozoic HelmintJiochiton Salter, Priscochiton Billings, GrypJio- 

 chiton Gray, and several unpublished names of Dr. Cari)enter, all belong 

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

 (for instance Sulcocliiton Grayi Eyckholt) are not moUusks; many of 

 them being valves of Balani or fragments of isopod crustaceans. 



Iieptochiton cancellatus. 



Chiton cancellatus Sowerby (as ? of Leach MS.), Conch. 111. f. 104-5, 1839. 



Chiton alhiis Pulteney, nou Lin. fide Hauley. 



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 & Hauley, 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. Ivi, f. 1, 



1869. 

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

 Chiton Bissoi auct. not of Payraudeau. 

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



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

 f Lepidopleurus arcticus Sars, 1. c. p. 112, t. 7, f. 7 a-h. 

 ? = 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- 

 tioribiis, haud rectangulatis, apicibus nullis ; mucrone centrali, valde 

 elevato, sculptura ut in L. asello, sed granulis parum majoribus ; areis 

 centr. jjarum divergentibus, areis lat. satis definitis, \ix elevatis ; intus, 

 laminis sut. minimis, triangnlaribus ; sinu latissimo, marginibusque 

 valvarum a sculptura externa pauUulum crenulatis; sond, angusta, 

 squamuliis teniiibus, haud imbricatis, haud striulatis, dense obsita. 

 Lon. 6, Lat. 3 mm. Div. 80°. 



Hah. — British seas; ]S"orwegian coast in 50-100 fms.; Greenland; 

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

 «lrew); Dalmatia (Brusiua); Alaska, at Unalashka, Shumagins, Port 

 Etches, and Sitka Harbor, 0-100 fms. Dall ! Ninety-four specimens ex- 

 amined. 



This species "without careful inspection will usually be confounded 

 with small specimens of Trachydermon cdhus, but a glance at the scidp- 

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

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

 The differential characters are as follows : 



The pustules which constitute most of the sculptiu-e are arranged 

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



