4i8 



MOLLUSCS. 



attach themselves to other shells by their right valve, the left being ornamented 

 with radiating ridges. Among the other families, Anatina, Thracia, and Phola- 

 domya are interesting genera, the last on account of its rarity in the living condition, 

 and its numerous representatives in bygone ages. Brechites, or Aspergillum, is 

 remarkable, as it is only in the earliest stages of existence that it presents the 

 appearance of a normal bivalve. It subsequently forms an elongate tube, open at 



one end and 

 closed at the 

 other by a 

 frilled disc full 

 of holes, like 

 the rose of a 

 watering - pot ; 

 e mb r yonic 

 valves being 

 embedded in 



the surface near the rose. The illustration shows the contracted animal extracted 

 from the shell, (e) indicating the siphonal openings, (c) the mantle aperture, (b) the 

 anterior side, (a) the mantle, (d) foot opening. 



a B 



Brechites vaginiferus. 

 A, Animal contracted, withdrawn from shell ; B, Anterior end of the shell. 



Order Septibranchiata. 



The members of this group are readily distinguished by the circumstance that 

 the gills are transformed into a muscular septum, extending from the anterior 

 adductor to the separation of the two siphons, and surrounding the foot, with 

 which it is continuous. This septum presents symmetrical orifices. The siphons 

 are sometimes short, or more or less produced. There are two adductors, 

 and the mantle -edges are united at three points. There are two families, 

 namely, the Poromyidcv and Cuspidariidce. Of the former, Poromya has the 

 siphons short, unequal, separate, and surrounded by a tentacular fringe ; each 

 half of the septum having several groups of lamellae, separated by orifices ; the 

 foot being slender, long, and the palpi larger. The shells are often minutely 

 granular and somewhat pearly within. The species are small, few in number, 

 and mostly from very deep water. Silenia is a deep-water form, dredged in 1950 

 fathoms, about eleven hundred miles south-west of Australia, and also in the South 

 Atlantic at the enormous depth of 2650 fathoms. The Cuspidariidce is a more 

 extensive family, and although the species are nearly all small, some are elegant in 

 form, and prettily sculptured. The shells have been classified by characters derived 

 from modifications of the hinge, and the surface ornamentation. The siphons are 

 longer than in the Poromyidce and united with tentacular fringes at the ends ; the 

 foot is moderately long and pointed, the labial palpi are rudimentary or wanting, 

 and the branchial septum is pierced with isolated symmetrical orifices. The shells 

 are mostly transversely ovate, and produced posteriorly into a more or less elongate 

 rostrum. They are found in all seas, in depths ranging from a few fathoms to over 

 three miles. 



EDGAR A. SMITH. 



