58 THE VOYAGE OF H.M.S. CHALLENGER, 



geutly convex, with acute cardinal extremities, and either gently rounded or nearly 

 straight in front. Ventral valve rather deeper than the opposite one. Beak pro- 

 minent, nearly straight, with a wide triangular area ; foramen large, incomplete, margined 

 laterally by narrow deltidial plates. Surface in each valve ornamented with about 

 twelve rounded corresponding ribs, the two central ones generally deviating so as to 

 admit a short, smaller one between them. Three or five sub-marginal septa, the three 

 central ones being, at the same time, the largest and most prominent. The loop is com- 

 posed of a single ribband-shaped lamella, which is first attached to the hinge-plate, and 

 afterwards forms a semicircular curve, lying close to the bottom of the shell in the 

 spaces intervening between the septa, to which it likewise adheres. Brachial appen- 

 dages folded into two or four lobes, united by a membrane, forming a brachial disk, 

 fringed with long cirri, mantle extending to the margins of the valves, closely adherent. 

 Shell structure perforated by numerous canals. Length 5, width 0, depth 3 mm. 



Habitat. — Argiope decollata was dredged alive in great abundance by the Challenger 

 Expedition, at Gomera, off Tenerifi'e, adhering to Megerlia truncata, on February 10, 

 1873, in 70 or 75 fathoms. 



Mr MacAndrew states that he obtained it off the Island of Madeira in 20 fathoms 

 (Geog. Dist. of Tert. MoUusca, p. 39, 1854). Professor E. Forbes dredged it in 1841 

 in the ^Egean Sea, in a range of from 27 to 110 fathoms (Report on the Mollusca and 

 Eadiata of the -iEgean Sea, p. 141, 1844). Costa observes that it generally accom- 

 panies Terebratulina caput-serpentis in the Mediterranean, and occurs plentifully near 

 the Islands of Capri, Ischia, Palmieri, and in the Gulf of Taranto. Jefireys states that 

 it is found at depths varying from 20 to 60 fathoms. Mr Fischer mentions, in the supple- 

 ment to his paper on the Brachiopodes des Cotes Oceaniques de la France (Journal de 

 Conchyliologie, 1871), that he dredged it off Cape Breton, in upwards of 45 fathoms. Dr 

 Jefireys quotes it from two miles east of Guernsey, in 18 fathoms It has also been 

 found in the Atlantic, coast of Spain, in 80 fathoms. 



It abounds in the Pliocene deposits of Sicily, at Nice, and elsewhere, also in rocks of 

 the Miocene group. 



Observations. — Dr S. P. Woodward and myself were able to give the first description 

 and illustration of the manner in which the loop and brachial appendages are arranged 

 in this important genus and species (Annals and Mag. Nat. Hist., vol. iv.. May 1852). 

 Since then, Dr Gray has proposed to separate from the genus Argiope all those forms 

 with a single sub-marginal septum, uniting them in the sub-genus Cistella. This view 

 has since been adopted by the larger number of malacologists, but by so doing the genus 

 Argiope would, up to the present time, be represented by the single species under 

 description. Externally Cistella barettiana, Dav. = Argiope antillarum, Crosse, so com- 

 pletely resembles Argiope decollata that it would hardly be possible to distinguish it. 

 In Cistella neapolitana, Cistella cuneata, Cistella ivoodivardiana, Cistella schrammi, and 



