16 AMPHINEURA. [Polyplacophora. 



Genus 1. MOPALIA, Gray, 1847. 



Mopalia, Gray, P.Z.S., 1847, 65, 69, 169 (exclusive of section xx). Type : 

 Chiton Hindsii, Sowerby. Molpcdia, Gray, 1857 (err. typ. ). Osteochiton, 

 Ball, 1886. 



Valves normally proportioned, transverse, not beaked, exposed, 

 the girdle somewhat encroaching at the sutures. Sinus small ; in- 

 sertion plate of anterior valve rather long, sharp, slit into nearly 

 smooth teeth, which are somewhat thickened at the edges of the slits, 

 the latter being normally 8 in number and corresponding in position 

 to external ribs. Median valves having similar 1-slit insertion plates. 

 Posterior valve depressed, the mucro post-median, insertion plate 

 rather sharp, smooth or roughened, having an oblique slit on each side 

 (rarely doubled) and a larger sinus in the middle behind. Girdle 

 wider at the sides than in front, leathery, more or less hairy, the hairs 

 simple ; with or without sutural pores. 



The genus is known only from the shores of the northern Pacific, 

 extending from Lower California to Alaska and Japan. It may be 

 regarded as the most primitive of the existing genera of Mopaliidce, 

 Placiphorella and Plaxiphora being special modifications of the Mopalia 

 type. The small additional slits occurring in some forms are cases 

 of partial reversion to the multifissate ancestral form which gave 

 rise to the family. (Pilsbry.) 



Our species is the first recorded from the Southern Hemisphere. 



1. Mopalia australis, Suter, 1907. Plate 3, figs. 12, 12a. 

 Mopalia australis, Suter, P. Mai. S., vii. 215, pi. 18, f. 12. 



Shell very small, elongately oval, with a blackish leathery girdle 

 and sutural tufts. Anterior valve with 8 slits, teeth smooth. Inter- 

 mediate valves with a rounded central posterior projection, insertion 

 plates with 1 slit on each side. Posterior valve depressed, with an 

 oblique slit on each side and bisinuate in the middle behind. Girdle 

 narrow, leathery, slightly broader on the sides, with a few sutural 

 bristles. Colour probably ash-grey, with a few longitudinal brown 

 stripes over the jugum. Interior bluish-grey, with a posterior brown 

 margin ; on the intermediate valves the tegmentum forms a narrow 

 band by passing beyond the articulamentum ; sinus broad and slightly 

 pectinate ; the sutural laminae narrowly rounded ; the valve-callus 

 is quite distinct. 



Length, 9 mm. ; breadth, 5'5 mm. Divergence, about 120. 



Type in my collection. 



Hob. Snares Islands (Captain Bollons). 



Remarks. I am indebted to Captain Bollons for two specimens 

 he collected at the Snares Islands. Both examples are so much 

 corroded that it is impossible to recognise any sculpture, if it was 

 present. The side slits of the posterior valve leave no doubt about 

 the generic position. 



