412 DR. GWYN JEFFREYS ON MOLLUSCA OF THE [Apr. 16, 



fide Dall). The habitat given by Linne, " in pelago Norvegico," ia 

 erroneous, so far as we at present know or believe, as well as 

 " Torquay " on Dr. Turton's authority. 



Very common and not less variable. Some specimens, especially 

 the young, are more or less acutely triangular ; others are nearly 

 ribless or smooth ; the very young have merely a moderately large 

 byssal orifice in the lower valve, the beak of the upper valve being 

 pointed ; and the loop is annular as in the subgenus Terebratulina. 

 This is a case of progressive development, and the reverse of what 

 takes place in Terebratula septata. The skeleton is distorted in the 

 monstrous form or variety. The size given by Deshayes for his 

 Morrisia gigantea scarcely exceeds one half of some ' Porcupine ' 

 specimens from 266 fathoms. 



There are six other synonyms, but obsolete. Terebratula (after- 

 wards Orthis) lunifera of Philippi, Forbes, and Costa is the young ; 

 the skeleton being imperfect or broken causes the appearance denoted 

 by that specific name. Mr. G. B. Sowerby, jun., figured in his 

 ' Thesaurus ' a ribless variety otArgiope cuneata as Philippi's species. 

 The distorted variety, which Scacchi at first described as Terebra- 

 tula monstruosa, but subsequently called " Antecedents varietas " 

 with reference to the present species, is the Morrisia davidsoni of 

 Eudes Deslongchamps ; it not unfrequently occurs with the normal 

 and intermediate forms. 



Seguenza in 1865 classified " Megerlea" as a subgenus of Tere- 

 br at ell a. 



Genus VI. Thecidea. 



Thecidea mediterranea, Risso. 



T. mediterranea, Risso, Hist. Nat. de l'Eur. me'rid. iv. p. 394, f. 185. 



Mediterranean, especially the African coasts, 30-300 f. Jamaica, 

 60 and 150 f. (Barrett, "fide Davidson). Mauritius (Sir Henry 

 Barkly) ! 



Thecidea spondylea of Scacchi, and probably T. testudinaria of 



Michelotti. 



B. Imperforate. 

 Family II. Rhynchonellid*. 

 Genus I. Atretia. 

 Atretia gnomon, Jeffreys. (Plate XXIII. fig. 4.) 

 A. gnomon, Jeffr. Proc. R. S. no. 121, 18th Nov. 1869, p. 121 ; 

 Ann. & Mag. N. H. Sept. 1876, p. 251. 



'Porcupine' Exp., 1869: St. 20, 1443 f. ; 30, 1380 f. 

 'Valorous' Exp.: Davis Strait, 1100-1750 f . ; North Atlantic, 

 1450 f. Norwegian Arctic Exp., 1877 : about thirty miles west of 

 " Tromso," on the slope of the banks, "cold area," 650 f. (Friele) ! 

 According to Mr. Dall, Atretia is a synonym of Zittel's genus 

 Dimerella (Dunker and v. Meyer, Palaeont. 18/0, p. 220), which is 

 a Jurassic Brachiopod ; but, although it belongs to the same family, 



