418 Mr ANSTED, on A NEW GENUS 



few species of orthoceratites. If then, as there seems every reason to 

 suppose, the siphuncle is the most important character in the shells of 

 multilocular cephalopoda, this very great difference would of itself war- 

 rant the formation of a separate group. All the species from Cornwall 

 are provided with decidedly large apertures in the chambers, and in 

 all, these fininel-shaped tubes are easily seen, produced beyond the 

 septum about half way into the next chamber. 



But again, the markings on the shell which seem so useful in deter- 

 mining Count Miinster with regard to any doubtful cases, are in our 

 English species apparently not to be depended on. Our fossils are in 

 beautiful condition ; the actual shell certainly remains in one specimen at 

 least, and we can trace a succession of transverse strise marked with great 

 beauty and regularity upon it ; but although the casts of the chambers 

 may be separately examined, the nature and use of the lobes does not 

 quite appear. One thing is certain, they do 7iot correspond to the inter- 

 section of the septa and the shell, and in only one of three species do 

 thej' occur at all. Some idea of the form of a septum will be obtained 

 from Fig. 4, Plate YWl. which represents a side and front view of the 

 cast of a chamber belonging to a species not determined. 



Tlie technical description of the genus will be thus expressed : — a 

 discoid spiral multilocular shell ; sides nearly simple ; whorls contiguous, 

 the last not enveloping the rest. Septa transverse, numerous, concave 

 outwardly, and perforated on tlie ventral margin for a siphuncle. 



In order to determine the place of this genus among other shells 

 of cephalopods, it will be necessary to pay most attention to goniatite and 

 nautilus, as it is to these that the nearest approximation is made. Von ' 

 Buch gives as the character of the former group, the dorsal siphuncle 

 of the ammonite, comparatively small and delicate ; the lobes of the septa 

 completely deprived of lateral denticulations, and the stride of growth 

 resembling those of nautilus, in not being directed forwards, as in am- 

 monites, but reflected backwards. The nautilus is known by its usually 

 central and comparatively large siphuncle, and the greater or less envelope- 

 nient of the whorls of the spire by the last one formed. 



