172 DK. T. DAVIDSON ON EECENT BllACHIOPODA. 



a uarrow ridge-like septum of small elevation extends to about one third of the length 

 of the valve, and on each side of the septum on the bottom of the valve are situated the 

 quadruple impressions of the adductor muscle. Length 1 inch 1 line, breadth 1 inch, 

 depth 7 lines. 



Mab. English Channel, depth 690 fathoms (Gwyn Jeffreys) ; olf Cape St. Vincent 

 (' Talisman ' Expedition), depth 57^ fathoms. 



Obs. In 1870, during the ' Porcupine ' Expedition, Dr. Gwyn Jeffreys obtained, in the 

 chops of the English Channel, one perfect living specimen and two incomplete valves of 

 a Bhynclionella which he thought might be the living representative of the fossil Plio- 

 cene Rlnjnchonella sicula of Seguenza, and he asked me to figure it for his paper published 

 in the ' Proceedings of the Zoological Society ' for 1878. He says : — " The shape of the 

 Sicilian fossil is rather more broadly triangular, and is viuiformly convex ; but it agrees 

 with the recent specimen in its peculiar structure, want of flexuosity in the front margin, 

 short beak, and small foramen. The fibrous texture of the shell is much softer and 

 looser than that of i^. imttaceay He adds that the " body is whitish, gelatinous ; mantle 

 not furnished at its edge with setae or bristles, as is the case in the Terebratulidae ; 

 arms fringed with short cirj-i, which are unequal in length and curl inwards at their 

 extremities ; byssal plug (peduncle) small, cylindrical, and slender ; its outer case or 

 sheath is chitinous, and resists the action of liquor potassye." 



I have seen only three examples of the recent shell ; they are, however, much 

 larger than the specimens of H. sicula that have been forwarded by Signor Seguenza 

 for my examination. Dr. P. Eischer has also written to me that he thinks the iden- 

 tification of the recent form with the fossil one is so uncertain that he proposes to 

 give it the distinctive name of cornea, which I have therefore provisionally adopted. The 

 specimens dredged off Cape St. Viucftnt by the ' Talisman ' Expedition are larger than 

 those obtained by Dr. Gwyn Jeffreys in 1870. 



09. Rhynchonella Doderleini, Davidson. (Plate XXV. figs. 14, 15.) 



Rhynchonella DUderleiiii, Davidson, Ann. & Mag. Nat. Hist. 5tli ser. vol. svii. p. 1, 1886. 



Shell transversely subpentagonal, wider than long ; hinge-line obtusely angular. 

 Dorsal valve deep, posteriorly uniformly convex, anteriorly divided into three lobes, the 

 central one forming a broad rounded mesial fold varying in elevation according to the 

 age of the individual. Ventral valve much less deep than the dorsal one, with a broad 

 mesial sinus of greater or less depth, commencing at a third of the length of the shell 

 and extending to the front. Beak moderately produced, almost erect, with an oval- 

 shaped foramen situated under its gently incurved angular extremity, and margined by 

 narrow deltidial plates. Lateral margins of the valves slightly sinuated, and forming in 

 front a more or less elevated curve. Surface of valves marked with numerous delicate 

 radiating ribs, with interspaces between them of almost equal width, and increasing in 

 number at variable distances from the beaks by the interpolation of shorter riblets. 

 Ribs numbering, in full-grown specimens, sixty, close to the margin. Valves closely 

 crossed by numerous equidistant, concentric, raised or foliated lines of growth, giving rise 

 at the margin on each riblet to short sloping or erect hollow spinules. Sliell-structure 



