ARGIOPE. 101 



belonging to the Essen species ; that they were identical with those he had published in 

 1842, under the names of Orthis {Arc/lope) Bronnii and 0. {Argiope) Buchii. This view 

 may probably prove correct, and I may have been led into error from having placed too 

 much value on the fact, that many individuals of the Chalk species possess ten costge, and 

 thus so far agreeing with Roemer's Green Sand species. In 1852, I was acquainted with 

 no other British species or specimens of Argiope lower down than the Soft or Upper Chalk, 

 but since that period, I have been able to examine several others from the Lower Chalk 

 of Kent and Upper Green Sands of Warminster and Cambridge. It will therefore be 

 desirable to reconsider our British Cretaceous Argiopes. 



48. Argiope Megatrema, Sowerby, Sp. Plate XII, figs. 31 — 32, and 34 — 36. 



Terebratula megatrema, Sowerby, in Fitton. Trans. Geol. Soc, vol. iv, 2d series, 



p. 343, pi. xviii, fig. 3 (read in 1827, printed in 1836.) 



— — Morris. Catalogue, 1836. 



— decemcostata, Roemer. Vers. Nord. Kreid, p. 41, tab. 13, 1840. 



— megatrema, Bronn. Index Pal., p.. 1241, 1848. 



— — D 'Orbigny. Prodrome, vol. ii, p. 172, 1850. 



— — A Cat. of the Terebratulse in the British Museum, p. 56, 1853. 



— decemcostata, Br. Fr. Roemer. Die Kreid, Westphalans, p. 71, 1854. 



Diagnosis. Shell transversely obovate, or obtusely pentagonal ; valves almost equally 

 and moderately convex, deepest near the umbo ; beak produced, nearly straight, truncated 

 by an oblique and large foramen ; beak ridges defined, leaving between them and the hinge 

 line a more or less developed triangular area; hinge line as long or shorter than the 

 greatest width of the shell. The external surface of each valve is ornamented by from ten 

 to twelve ribs, with flattened interspaces between. The costae correspond in each valve, 

 a few smaller ones being intercalated between the larger ones near the frontal margin. In 

 the interior of the dorsal valve, the loop first fixed to the base of the dental sockets is 

 folded into two lobes, and attached to a single mesial plate. 1 Length 2|, width 3, depth 

 1^ lines. 



Obs. So rare is this little shell, that for many years I was unable to trace a single 

 example ; and it was only during a recent visit to the Bristol Institution Museum, that I 

 had the good fortune to discover in that collection one example, which proved, on 

 examination, to agree with the shell described and figured by Sowerby, in the ' Geological 

 Transactions :' it is a true Argiope, not a Terebratula, as generally supposed. Roemer's 

 figure of A. decemcostata, PL XII., fig. 35, and another, fig. 36, furnished by M. de 

 Hagenow, might at first sight indicate a distinct species on account of the length of the 

 hinge line and area, but having recently received from Dr.Pr. Roemer a specimen collected 



1 The interior of this species has been admirably described and figured by M. Suess, in bis excellent 

 memoir entitled ' Ueber dieBrachial-Vorrichtung bei den Thecideen,' pi. iii, fig. 1 (Aus dem Decemberhefte 

 des Jahrganges, 1853) der Sitzungsberichte der mathem-naturw. Classe der kais Akademie der Wissen- 

 schaften (xi Bd., s. 991), besonders abgedruckt. 



