NERIN^A. 195 



Where the ornaments have been preserved we find very fine spiral lines, whose 

 granulations can only be seen under a lens of some power ; these lines have a 

 tendency to die out in the more mature whorls. Rich tubercular ornamentation 

 is rare, and would seem mainly confined to species from the highest beds of the 

 Lincolnshire Limestone, which appear to have Bathonian afiinities. The mature 

 whorls sometimes show the curving lines of growth and the slight raised line on 

 the posterior margins, but too often almost every surface feature is obscured.^ 



Although there is considerable uniformity in the section of an individual 

 Nerinsea, that is to say, that the folds vary but little in the several whorls, yet there 

 does seem a tendency in many cases for the mature whorls to be less restricted as 

 to internal space. It may be that the folds of the body-whorl were more or less 

 absorbed, so as to give the animal additional space. I have noticed, especially in 

 PtijgmaUs, this tendency of the folds to diminish, and indeed to become almost 

 effete in the body-whorl. Mr. Witchell also noticed this feature, and attributed it 

 to wear. It is not a little singular that when we obtain an unbroken shell, as is 

 frequently the case in the Oolite Marl horizon, there is no trace of folds to be 

 found, either on the lip or columella. 



Definition and Range of Species. — When Lycett wrote ' The Cotteswold Hills,' 

 in 1857, he enumerated no more than six species of Nerinsea in the Inferior Oolite 

 of the Cotteswolds. In 1887 Witchell had brought up the number to twenty. In 

 the present Monograph certain forms have been named provisionally, but not 

 described as distinct species. Some of the forms described as species to a certain 

 extent run into each other, and it may be predicted that future collectors are sure 

 to find an increased number of intermediate forms. Moreover, many of the 

 species appear to be local, and often limited in range. A few are useful as indi- 

 cating horizon, but it would seem as though still fewer could be relied upon for 

 any great distance. The most marked Nerinsean horizon known to me is that of 

 N. Ouisei in the Chjpeus-grit. The varieties of N. Cotteswoldise also help to 

 connect both the Pea-grit and Oolite Marl with certain horizons in the Lincolnshire 

 Limestone. 



Nerinseas of the Lincolnshire Limestone. — To a certain extent these require 

 separate treatment, especially as regards specimens from Weldon and Great 

 Ponton. The species at Weldon are extremely numerous, including examples of 

 Nerinella, Nerinsea, and Ptygmatis, though Nerinsea greatly preponderates. Many 

 are very small, and nearly all have suffered either before or since mineralization. 

 There seems to be a great admixture, suggesting the possibility of some of the 



1 Aa regards ornamentation it is curious to note what different artistic treatment has been 

 accorded to the same species. Thus, N. funiculus, Desl., N. clavus, Desl., N. pseudoci/lindriea, D'Orb., 

 are represented in Deslongchamps' work as having fine spiral ornamentation, whilst in D'Orbigny's 

 figures of the same species the spiral ornamentation is entirely ignored, and a very elaborate system of 

 grototh-lines is substituted. 



