EXPLANATION OF PLATE 28. 49 



Fig. 4. Convex upper surface of portion of another re- 

 cent pen, of the same kind. The structure of figs. 

 3 and 4 closely resembles that of the fossil species 

 represented at fig. 6, of this same Plate, and also 

 at PI. 29. fig. 1. and PI. 30. In all of them, the 

 horny plates are composed of a series of longitudi- 

 nal fibres, intersected by another series of transverse 

 fibres. The disposition of the transverse fibres is 

 most simple in the recent species ; passing obliquely 

 outwards from each side of the central shaft, like 

 the barbs or fibrils in the vane of a feather, and being 

 the most distinct towards the outer margin. 



The longitudinal fibres are scarcely visible in the 

 recent species, except where they are collected into 

 fluted fasciculi, PI. 28. fig. 4. BB.) in those parts 

 which correspond with the marginal bands of the 

 fossil species. (Original.) 



C. Central part of the Pen, raised like the shaft of a quill 

 between its fibrils. 



Fig. 5. Ink bag of a recent Cuttle fish, dissected by 

 the author at Lyme Regis, 1829, containing its na- 

 tural Ink in a desiccated state ; it is a black shining 

 Jet-like substance, having a splintery fracture, and 

 resembling the substance and fracture of the fossil 

 Ink. Its bulk is not much reduced by desiccation. 

 (Original.) 



Fig. 6. Upper convex surface of a fossil pen of Loligo 

 Aalensis from the Lias of Lyme Regis. A. A. the 

 barbs; B.B. the marginal bands; C. axis of the 

 shaft; D. excretory duct of the Ink bag, distended 

 with petrified Ink.* (Original.) 



* In this specimen we see distinctly the disposition of the marginal 

 bands. 



VOL. II. 5 



