PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 315 



Microplaz H. Adams. 



Resembling Chitonellus externally ; submerged laminEe unslit, entire, fused in an 

 undistinguishable manner with the parts -svhich usually constitute the sutural 

 laminae. M. Grayi Ad. & Ang. 



The paleozoic HelmintfiocMton Salter, PriscocMton 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 chiton Gray, and several unpublished names of Dr.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 Eyckholt) are not mollusks ; 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, 1839. 



Ckitan alius Pulteney, uon Lin. fide Hanley. 



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



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



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



(outlines inverted in figure). 

 Leptochiton cancellatus H. «fe A. Adams, Gen. Rec. Moll, i, p. 475, 1854. 

 Chiton cancellatus Jefireys, 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. 

 Lcpidopleurus 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 Gmeliu, S. N. 3206, 1788.— Schroter, Einl. iii, p. 509.— 



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



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

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

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

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

 centr. x)arum divergentibus, areis lat. satis definitis, \ix elevatis ; intus, 

 laminis sut. minimis, triangularibus; sinu latissimo, marginibusque 

 valvarum a sculptura externa pauUulum crenulatis; zona, angusta, 

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

 Lon. 6, Lat. 3 mm. Div. SQo. 



Hah. — British seas; ISTorwegian coast in 50-100 fms.; Greenland; 

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

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

 Etches, and Sitka Harbor, G-lOO fms. Dall ! Ninety-four specimens ex- 

 amined. 



This species without careful inspection will usually be confounded 

 with small specimens of Trachydermon alhus, 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 maguitier is indispensable. 

 The differential characters arc as follows : 



The pustules which constitute most of the sculpture are arranged 

 like overlapi)ing coins or a solid-linked chain in lines which in the dor- 



