50 THE VOYAGE OF H.M.S. CHALLENGER. 



Megerlia truncata, Linne (PL III. figs. 15-18). 



Anomia truncata, Lin., Syst. Nat., 1152. Born, Chemnitz, Gmelin, DiUwyn, PoU, &c. 



Terehratida truncata, Eetz, n. gen., p. 14. Lamarck, Sowerby, Blainville, Costa, and others. 



Terebratella truncata, D'Orh., Ann. Sci. Nat., 1848, vol. viii., pi. vii. figs. 11, 12, 16, 37. 



Terebratula monstruosa, Scacchi, Osser. Zool, vol. ii. p. 1. 



Anomia discidus, PaUas, Misc. Zool., p. 184, pi. xi. fig. 1. 



Terebratula disculus, Blainville, Die. Sci. Nat., vol. liii. p. 138. 



Ortliis truncata, Philippi, Moll. Sicil., vol. ii. p. 69. 



Terebratula oblita, Mick. Brach. Fauna Misc., pi. ii. fig. 21. 



Meganthyris oblita, D'Orb, Prodrome, vol. iii. p. 134. 



Terebrcdida scobinata, Gmelin; Terehrcdida decusscda.,'S>\&mv.; Terebratula irregularis, Blainv.; vide 



Reeve. 

 Megerlia truncata. King, Perm. Foss., p. 145. Davidson, Gray, Reeve, Woodward, Chemnitz, Suess, 



Dall, H. & A. Adams, Jeffreys, Monterosato, and the generality of modern authors. 

 Morrisia gigantea, Deshayes, Cat. des MoU. de I'lle de la Reunion (Bourbon) annexe E., p. 37, 



pi. xxxii. figs. 9-11. 



Shell transversely oval or semicircular, somewhat depressed, fulvous white. Hinge-line 

 nearly straight. Dorsal valve gently convex, mesially longitudinally depressed from close 

 to the umbo to the front. Ventral valve deeper than the dorsal one, and longitudinally 

 keeled. Beak very slightly incurved, and truncated by a large circular incomplete 

 foramen, with two small deltidial plates, area flat, sharply defined. Surface of valves 

 marked with numerous fine pustulate radiating riblets, increased in number at variable 

 distances from the beaks by the intercalation of shorter ribs. Surface crossed by con- 

 centric lines of growth. Shell structure perforated by minute canals. Loop trebl}' 

 attached, first to the base of hinge-pla,te, to the median short septum, and again by 

 lateral branches departing from the reflected upper part of the loop to the upper anterior 

 extremity of the septum. Brachial or labial appendages forming two ear-shaped pro- 

 cesses, connected by a membrane forming two large lateral lobes and a short median 

 sjDiral one. Dimensions, length 13, width 14, depth 6 mm. (Some Mediterranean 

 examples have exceeded these proportions by a third.) 



Habitat. — This species was dredged in great profusion by the Challenger Expedition 

 ofi" Gomera, Teneriffe, on February 10, 1873, in 70 or 75 fathoms, with Argiope 

 decollata adhering to it. It seems to enjoy a very extended geographical range. It 

 occurs in the Mediterranean, and abounds on the adjacent Atlantic shores. Signor Costa 

 obtained it from near the Island of Capri, Ischia, Palmieri, and the Gulf of Taranto. 

 E. Forbes in his report on the Mollusca of the ^gean Sea, 1844, found it living at 

 from 60 to 105 fathoms. It was also dredged oft' the coast of France, Morbihan, He de 

 Noirmoutier in Vendee, Guetaria, North Spain. Mr Dall mentions, that a specimen 

 under the name of Megerlia tnmcata was sent to the Smithsonian Cabinet with the 

 habitat of New South Wales, but this locality requires further confirmation, especially 

 as Mr Dall observes that " the spiral lobe of the branchia, prominent in the Eurojoean 

 species, seemed to be nearly wanting in the Australian shell, the fringes in the former 



