Hyatt.] 372 [June 7, 



lines drawn between the different species being so slight that they 

 vary with every locality. Contractual can only be separated from 

 subcoronalum by the fineness of the ribs on the abdomen, and in the 

 adult by the aspect of the sides. The connection with subcoronatum 

 is largely made through the young, which are indistinguishable from 

 the young of that species in some specimens. 



The Herveyi-like, or macrocephalum-like forms of contr actum occur- 

 ring in the Parkinsoni-bed, have finer ribs than Herveyi, but it is 

 probable that they vary greatly in this respect. The young of Steph. 

 Herveyi are in some varieties tuberculated, but acquire the aspect and 

 characteristics of the adult of Steph. contractum, including the fine 

 abdominal ribs, as soon as they lose their tubercles. Others which 

 have no tubercles acquire this aspect at still earlier age, and these 

 lead into Steph. macrocephalum, in which the young are invariably 

 smooth, or not tuberculated. 



In Steph. macrocephalum we find a series of forms, which become 

 gradually more and more compressed laterally, until they present a 

 very narrow abdomen and whorls of extraordinary breadth. The 

 abdomen, however, does not become sharp, even in extreme varieties. 



Throughout this series, as a rule, only the oldest specimens become 

 smooth on the latter part of the living chamber, showing that this is 

 an old age characteristic. The growth maintains the same ratio of 

 increase in the size of the animal throughout life, and the whorl 

 therefore never becomes contracted even in extreme old age. There 

 is, however, here, as in the compressed forms of other series, a notic- 

 able decrease in the size of the species or varieties as a whole. The 

 laterally compressed forms are usually much smaller than the 

 broad abdomened forms, a fact in direct accordance with the idea 

 that they are the senile descendants of the broader forms. 



The mouths of this series, like those of all species previously de- 

 scribed, present no lappets at any stage of growth, and are very uni- 

 form in outline. 



Steph. Brocchii is a species with vary peculiar characteristics, and 

 its affinities lead in two directions; one towards Steph. platystomum, 

 and the other towards Steph. Gervilii, and other senile forms. 



Some of the varieties do not appear to contract the living chamber 

 at all, or only the very last portion near the mouth. These have the 

 precise aspect of the young of the finer ribbed varieties of Herveyi. 

 Others show this contraction in such a marked manner that the in- 



