﻿BEITISH FOSSIL CEPHALOPODA. 165 



prolongation appears to have had a separate sheath on the inside, as it is not marked 

 in any way by the septa, but has upon its distal surface longitudinal lines bounded 

 by three deeper furrows, as though they were muscular impressions. These 

 impressions are very similar to those found in the little internal lobe of the recent 

 Nautilus, to which this prolongation is possibly homologous. The septa are direct, 

 and distant about ^ the diameter ; their convexity is \ of the same. They are very 

 little affected by the lateral tube, those nearest the body-chamber bending down 

 slightly as they embrace it, but not so much as to reach the next septum. The 

 siphuncle is situated about f across the diameter, in the same radius as the lateral 

 tube. Its swollen diameter is 5 lines, thus reaching to within 1 line of the tube, 

 but it contracts to half its size at the septa. Its bulbous exterior is granular. The 

 length preserved is about 3 inches, and the greatest diameter 3^- inches. From 

 the Lower Llandovery rocks of Llandovery. In the Museum of the Geological 

 Society. 



General Description. — No other specimen has yet appeared showing any similar 

 peculiar features, and therefore but little additional information can be obtained on 

 their meaning ; but as this is a large specimen, we are led to ask if smaller ones 

 cannot be found which might develop this form of body-chamber. The form 

 described by Woodward as Actinoceras baccatum appears to answer this requirement 

 exactly. It is of somewhat, but not considerably, smaller size ; its rate of increase 

 rather greater. The number and convexity of the septa ; the position, size, and above 

 all the character, of the siphuncle — nearly spherical in both — all are consonant 

 with the idea of its identity with the species at present under description : certainly 

 there is nothing to distinguish them in the parts that are comparable. I have not 

 been able to examine the original of A. baccatum, but a more instructive example in 

 Dr. G-rindrod's collection (fig. 4) shows the much greater thickness of the organic 

 deposits on the septa in the earlier than in the later part of the shell : this is seen 

 by the septa being represented by wide gaps below, but narrow ones above, and, 

 more important, the folds of the internal siphuncular membrane dividing the cavity 

 into four, of which there is some appearance also in fig. 36. 



Distribution. — In the Lower Llandovery Beds, Llandovery (1), and in the lowest 

 Woolhope Beds, Woolhope (2). 



Subgenus Oonoceras. 

 Orthoceras (Conoceras) eoum, Blake, PI. XYI. figs. 5, 5a.. 



Syn. 1S66. Endoceeas eoum, Wyatt-Edgell, ' Geol. Mag.' vol. iii. p. 161 (name only). 



Type. — The section is not seen, and the rate of increase is very small ; never^ 

 theless the larger end of the specimen may be pretty satisfactorily made out. The 



