90 CARBONIFEROUS CEPHALOPODA OF IRELAND. 



about half its length, has fine longitudinal ridges, one of which is continuous and 

 forms the inner keel of the umbilicus. At the commencement of the second 

 whorl the periphery bears on each side of the median area two keels, which 

 gradually become obsolete, sometimes near the base of the body-chamber, where 

 they may be represented merely by faint, slightly raised lines, sometimes extend- 

 ing nearer to the aperture. The periphery, losing the keels, here becomes rounded 

 at the umbilical angles. 



The two keels encircling the whorls are finely crenulated, at least up to the 

 termination of the first whorl, and often as far as the extremity of the second, 

 after which the crenulations disappear and the keels become simple. 



The test, when suitably preserved, is seen to be covered with fine transverse 

 lines of growth ; of these lines, stronger ones occur at regular intervals and 

 develop slight nodes in crossing the- umbilical keels, thus giving rise to the 

 beautiful crenulations just described. These crenulations do not appear to be 

 developed upon the peripheral keels. Extremely fine lines, taking a longitudinal 

 direction, cover the lines of growth; these are irregular and minutely tortuous in 

 their course, and of silky fineness. They can be seen only Avith the aid of a lens. 



The rarity of the preservation of such ornaments as these latter is probably 

 due to the abrasion which the dead shell undergoes on the sea-bottom before 

 being covered by the protecting mud. In some cases, perhaps in the majority of 

 them, mineral or chemical action has probably operated in the obliteration of such 

 delicate markings, when the deposit in which the fossils were entombed had 

 become consolidated into rock. 



Affinities. — The close resemblance between this species and V. paucicarlnatus, 

 Foord, is obvious upon comparing the figures of them (PI. XXIV, and PI. XXV, 

 figs. 3 a, h) ; it would be scarcely possible to distinguish between them without 

 the septa being exposed to view. 



On comparing the septation of the present species with that of V. pauci- 

 carinatus, it is found that it is much closer ia the latter species, in which the septa 

 vary from 6*5 mm. to 8*5 mm., where the width of the peripheral area is from 

 50 mm. to 55 mm. It has just been stated that the septa in V. jyingnis a,re 10 mm. 

 apart where the width of the peripheral area is 40 mm. There is thus a very great 

 difference in this respect between the two species. 



Another feature in which V. plnrjuis differs from V. paucicarinatns is in the 

 absence of the annular lobe conspicuous in the last-named species (cf. de Kon., 

 ' Calc. Carb.,' loc. cit., pi. xxviii, figs. 5 a, h; pi. xxx, fig. 6 c). 



Hemarl's. — I have seen very few specimens of this species which could be 

 identified as such, but, as I have already indicated, the presence of the test would 

 render its identification difficult, if not impracticable ; therefore some specimens 



