180 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



ASCOCERAS. 



As an interesting addition to the fauna of our Upper Silurian 

 rocks, I subjoin a description of a species of the genus Ascocerus 

 above quoted, p. 168. Three or four specimens have occurred in the 

 Upper Ludlow rock, both from near the town of Ludlow, and from 

 Herefordshire. It appears to be a larger and thicker species than the 

 A. Bohemicum, Barr., and I propose to call it 



Ascoceras Barrandii, spec. nov. PI. XII. fig. 7. 



A. clavatum, longi-ovatum, cylindricura ?, lente curvatum, striis transversis tenu- 

 issimis obliquis ; septis ut in A. Bohemieo. 



Our species differs from M. Barrande's A. Bohemicum * chiefly^by 

 the considerable obliquity of the lines of growth. The form is some- 

 what more inflated, and the region occupied by the septa, if possible, 

 more extravagantly sigmoidal in outline. Our specimen shows the 

 surface of the penultimate 1 f septum and the place of the siphuncle. 



Although here described as a distinct species, it is possible that 

 more specimens may prove it to be identical with the Bohemian 

 fossil. Our specimens are flattened ; and the greater obliquity of 

 the lines of growth may be due to this circumstance. 



Locality. Upper Ludlow rock, Ludlow (collected by Mr. Light- 

 body and Mr. J. Harley of Ludlow) ; at Stansbatch, Herefordshire 

 (collected by Mr. J. E. Davis of Presteign), now in the Museum of 

 the Geological Survey. I found one also at Hales End, Malvern ; it 

 is now in the cabinet of my friend R. B. Grindrod, LL.D., F.G.S., 

 of that place. It appears to occur in the very uppermost layers of 

 the Ludlow rock, immediately beneath the Bone-bed. Its place in 

 Bohemia is lower down (in " Etage E." or the Wenlock-beds) . In 

 North America again, as I learn by a letter from M. Barrande, the 

 genus has occurred in the "Hudson River Group" (Caradoc Sand- 

 stone)! 



EXPLANATION OF PLATE XII. 



Fig. 1. Tretoceras bisiphonatum, Sow. sp. ; natural size. In the Museum of the 

 Geological Society, a, shows the flattened and decurrent edges of 

 the septa where they join the lateral tuhe. b, the cast of the tube 

 itself undivided by any constrictions, c, the beaded siphuncle placed 

 excentrically. 



2. A restored figure : a portion of the shell is supposed to have been re- 



moved. 



3. End-view of one of the septa, showing the excentric position of the 



siphuncle. 



4. Outline of the septum of Nautiloceras paradoxicum, Sow., sp. ; to show 



the possible analogy of Tretoceras with this form, if the ends were 

 more incurved. 



5. Outline of the septum of Gonioceras anceps, Hall ; also for comparison. 



The shell, however, in both these forms would tine the whole concave 

 surface. 



6. Bactrites, Sandberger ; introduced to show the small ventral lobe in the 



septa. 



7. Ascoceras Barrandii, Salter, with septa added in dotted lines. 



* Bull. Soc. Geol. France, 2nd ser. vol. xii. pi. 5. fig. 20. 

 f There were clearly more than two ordinary septa at the small end of the shell. 

 This is seen in some of M. Barrande's specimens now in the British Museum. 



