DE. T. DAVIDSON ON EECENT BEACHIOPODA. 105 



Shell transversely oval, semicircular or subquadrilateral, somewhat depressed, fulvous 

 white. Hinge-line nearly straight, nearly as long as the breadth of the shell, with acute 

 or rounded angles. Dorsal valve gently convex, sometimes much flattened, mesially 

 depressed longitudinally from the umbo to the front, more or less indented in front. 

 Ventral valve deeper than the dorsal one, and longitudinally keeled. Beak very little 

 inciu'ved, and truncated by a large circular incomplete foramen, margined anteriorly by 

 the umbo and by two small rudimentary lateral plates ; bcak-ridges sharply defined, 

 leaving between them and the hinge-line a flat area. Surface of valves marked with 

 numerous fine radiating riblets, increasing in number at variable distances from the 

 beaks by the interpolation of shorter riblets. Surface of valves crossed by concentiic 

 Lines of growth. Shell-structure perforated by minute canals. Loop extending to little 

 more than half the length of the valve, trebly attached, first to the base of the hinge- 

 plate, then to a short median 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 consisting of two ear-shaped processes connected by a membrane 

 forming two large lateral lobes and a short median spiral one. Length 9 lines, breadth 

 10, depth 6 lines. 



Sab. This species was dredged in great profusion by the ' Challenger ' Expedition off 

 Gomera, Tenerifi'e, in 70 or 75 fathoms. It is a common Mediterranean species, and 

 abounds on the Atlantic shores. Signer Costa obtained it from near the Island of Capri, 

 off Ischia, Palmieri, and in the Gulf of Taranto. Prof. E. Porbes states, in his Report on 

 the Mollusca of the ^gean Sea, 1844, that he found it living at from 60 to 105 fathoms. 

 It was also dredged off the coast of France, Morbihan, He de Noirmontier; Guetaria, 

 North Spain, off Marocco and the Canaries ('Talisman' Expedition), in from 50-65 fathoms. 

 The species has been quoted from New Soutli Wales, but I doubt the accuracy of this 

 statement, nor have I ever seen any specimens from Japanese waters. The habitat of 

 the Philippine Islands, given by Woodward, also requires corroboration. The specimen 

 figui-ed by Deshayes as having been di-edged off the Island of Bourbon (?) certainly belongs 

 to the species under description ; but it is erroneously named Morrisia gigantea, and its 

 habitat also requii-es confirmation. 



Megerlia truncata is a common fossil in the Upper Tertiary formations of Sicily, Italy, 

 Nice, and elsewhere. 



Ohs. This is an abundant and weU-known species, and the type of the genus Megerlia. 

 As may be seen from the long list of references, it has been often described, and very 

 generally so under the specific name of truncata. It bears a somewhat obscure external 

 resemblance to some forms of Orthis, but, although it has been several times referred to 

 that genus, it possesses none of its characters. In his admirable memoir entitled 

 ' Recherches sur I'Organisation du Manteauchez les Brachiopodes articules," 1864, M. E. 

 Deslongchamps describes with minute detail the mantle of several forms, and especially 

 that of Megerlia truncata. He states that the microscopic flattened spicula of tlie mantle 

 are still more abundant than in TerebratuUna, have a very peculiar shape, and that the 

 calcified portions are well defined in both valves. The flattened spicula are wide and 

 nearly quadi'ilateral, with rounded extremities, the edges being festooned; they form 



