MAGAS. 19 



Plate III, fig. 13. An enlarged illustration of the beak and worn umbo; a. Septum 



in smaller valve seen through the foramen. 



,, figs. 14, 15. Argiope decollata — recent species placed here to illustrate the 



three elevated dissepiments a and b . The loop is not intro- 

 duced, (see woodcut, Part I.) 



,, fig. 16. A profile view of the recent form, showing how close it lies to the 



object to which it is attached. 



Genus — Magas, Soioerby. 1818. 



Animal unknown ; fixed to marine bodies by a pedicle issuing out of the foramen of 

 the larger valve. Shell small, inequivalve, generally more or less regularly oval ; structure 

 punctuated ; beak truncated by a foramen, extending to the umbo of smaller valve ; hinge 

 articulating by means of two teeth in the larger and corresponding sockets in smaller 

 valve ; apophysary system in the imperforated valve composed of an elevated longitudinal 

 septum, reaching from one valve to the other, to which are affixed two pairs of calcareous 

 lamellae, differently disposed ; the lower pair are riband-shaped, attached first to the crural 

 base : they direct themselves by a gentle curve to near the anterior portion of the septum, 

 to the sides of which they are affixed ; the second pair arise on either side of the upper 

 edge of the septum, extending in the form of two triangular anchor-shaped lamellae. 



05s. I have fully described this genus under the species Magas pumilus, and therefore 

 must refer to it for further details. 



7. Magas pumilus, Sow. Plate II, figs. 1 — 12 and 33. 



Figured by Faujas in 1789, ' Histoire de la Montagne de St. Pierre de Maastricht,' 

 pi. xxvi, fig. 6 (but not named). 



Magas pumiltjs, Sow. Min. Conch., vol. ii, 1818, p. 40, tab. 119, figs. 1 — 5. 

 Terebratula concava 1 Lamarck. 1819. An. sans Vert., vol. vi, p. 251, No. 26. 



See likewise Dav., Annals and Mag. of Nat. Hist., 2d ser., 

 vol. v, June, 1850. 

 Magas pumilus, Parkinson. 1822. An Introduction to the Study of Organic Remains, 

 p. 227, pi. vii, fig. 14. 



— — Brongniart and Cuvier. Descript. Geol. des Env. de Paris, 1822, 



pi. iv, fig. 9. 



— — Defrance. 1823. Die. des Sci. Nat., vol. xxviii, p. 13, fig. 1. 



— — Blainville. 1826. Malacologie, pi. liv, fig. 1, (non Magas pumilus, 



Sow.) 



— truncata (Rose), Woodward. 1833. Outlines of the Geol. of Norfolk, tab. vi, 



fig. 9. 



