318 PKOCEEDINGS OF UNITED STATES NATJONAL MUSEUM. 



This specimen much resembles L. alveolus, to which I at first referred 

 it. A careful raicroscoj)ical examination, however, shows difi'erences 

 which I am disposed to consider specific; but I have but one specimen, 

 and others might show modifications in these particulars. 



The differential characters are as follows : In alveolus the pustules are 

 distributed evenly, closely, and in no pattern whatever, ail over the sur- 

 face. In Belkna])i, they are more widely separated, and arranged in quin- 

 cunx on the dorsum, the spaces seeming to radiate from the median 

 dorsal line. In alveolus, the lateral areas are barely perceptible ; in Bel- 

 Jcnapi, they are raised, concentrically rugose, and the pattern of the pus- 

 tular arrangement is different and more irregular than that on the dorsum. 

 In Bellaiapi, also, the girdle is very thin, narrow, and sparsely set with 

 small pellucid spicules near the margin. The posterior mucro, or apex of 

 the posterior plate, in BelJcnapi, is prominent, overhangs a shallow con- 

 cavity, and from its point there diverge anteriorly four depressed lines, 

 the outer two to the anterior lateral angles of the plate, the inner two 

 equidistant from each other and the outer lines. Between these lines 

 the plate is swelled, forming three rounded ridges, extending forward 

 like the leaflets of a trefoil or clover. Nothing resembling this has been 

 observed on any of the other species which have come under my notice. 



The soft parts, in spirits, appear to resemble the other species com- 

 pared with it. It is evidently adult. 



It was certainly unexpected that a stone-clinging mollusk hke a Chiton 

 should reach such great depths as those from which this was obtained. 

 In the same region, and at about the same depth, a Cyliehna and a 

 Natica, both apparently identical with certain Arctic species, were also 

 obtained in the same way. Its enormous range in latitude, as indicated 

 by the Kerguelen specimens, reminds one of the range of species in 

 earlier geological times, and points out how relatively modern our littoral 

 marine fauna? may be. It is not the only form common to the southern 

 and northern oceans. 



Extra-limital Species. 

 Iieptochiton asellus. 



Chiton asellus (Chemu. Speugl.) Lowe, Zocil. Joum. ii, p. 101, pi. v, f. 3, 4, 1825. 



Chiton cinereiis Montague, Tiirton, and others, not of Linn6. 



f Lepidopleurus cinereus Sars, 1. c. p. 112, pi. 7, f. 8 o-ft, 1878; as of Linn6. 



Hah. — Northern seas of Eiu'ope; Lofoten Ids.; Greenland? (Morch); 

 not New England, as erroneously stated by authors. The cinereus of 

 Linn6, from his tn>e, was a Trachydermon. 



Leptochiton fuliginatus. 



Chiton fuliginatua AA. & Rve. Conch. Icon. pi. xxvi, f. 174, 1847. 



Rah. — Korea, Belcher. 



Leptochiton conciuuus. 



Leptochiton condnnns GUI. Otia, p. 117, 1860. 



Hah. — Hakodadi, Japan ; Stimpson. 



