12 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 23 



Propeamussium meridionale (E. A. Smith) 1885 



Plate 1 



[non] Ainussiuin luciduin van striata Jeffreys, 1879, p. 562. " 'Porcu- 

 pine' Exp. 1870, Atl., St. 17a [off Cape Mondego, Portugal, in 795 

 fathoms]; 'Challenger' Exp. (off Marion I.) station 145; [see 

 below], 1375 fms." 

 Ainussiuin meridionale E. A. Smith, 1885, p. 316, pi. 24, figs. 1, la. 

 Challenger stations 146, 158, 302 [see Type locality and Geo- 

 graphical range]. 

 Holotype: British Museum. 



Type locality: Challenger station 158, 50°rS, 123°E, southern 

 Indian Ocean (about 1600 miles south of Cape Pasley, south coast of 

 Western Australia), in 1800 fathoms. 



Original description : Testa f ragilissima, paulo inaequivalvis, irides- 

 cens, pellucida, utrinque anguste hians. Valva dextra liris flliformibus 

 numerosis radiantibus, incrementique lineis concentricis ornata, sinistra 

 magis opaca concentrice lirata, liris tenuissimis, complanatis, sensim 

 accrescentibus. Auriculae subaequales, anticis interdum paulo majoribus. 

 Pagina interna nitida, iridescens, liris tenuissimis undenis instructa, in 

 valva dextra radiatim striata, striis cum liris externis congruentibus. 

 Van : Testa liris internis duodenis munita, valva dextra extus can- 

 cellata. 



This species is slightly oblique, excessively thin, a little inequivalve, 

 pellucid white, and narrowly gaping above on both sides. The right 

 [left] or deeper valve is more glossy than the left [right], and sculp- 

 tured with numerous very slender radiating lirae and concentric waves 

 and striae of growth. The other [right] valve is ornamented with close- 

 set very fine concentric shallow grooves and depressed ridges. The former 

 under the microscope exhibit a very minute reticulation, each parallel 

 zone of this fine network being connected with the one above and below 

 by elongated meshes passing over the intervening ridges. The auricles 

 are small, at times denticulated above, slightly unequal, the anterior 

 being rather larger than the posterior, or this proportion may be re- 

 versed. The beaks are moderately acute, the sides meeting at an angle 

 of about 115 degrees. The valves are glossy, somewhat iridescent within, 

 and strengthened with eleven fine lirae, the longest of which extends 

 about two-thirds across the interior. The right [left] valve is also very 

 finely striated, the striae corresponding to the slender lirae of the outer 

 surface. 



