Hyatt.] 368 [June 7, 



ticularly fine and numerous, the lateral ribs like those of Steph. lin- 

 guiferum or those of Steph. Deslongchampsii. These are apparently 

 identical with the plicatissimum of Quenstedt. Both of these forms, 

 Steph. plicatissimum and Steph. Deslongchampsii, are found in the 

 Parkinsoni-bed. 



Some of the varieties of Steph. subcoronatum are nearly identical 

 with Steph. nodosum, and some of them resemble closely the smaller 

 specimens of Steph. coronatum or Blagdeni. The forms from Dundry, 

 and also those alluded to in Quenstedt's descriptions of Humphriesi- 

 anus, as allied to Amm. Brocchii Sow., show a close series of transi- 

 tions from the finer ribbed specimens with open umbilici and young 

 like sub-coronatum to those with stouter whorls, no tubercles and 

 forms and ribs like true Brocchii. The more open umbilicated forms, 

 those like true nodosum in aspect, lead by a similar series of grada- 

 tions apparently into Braikenridgii, though here, of course, some 

 doubt must always intervene until the appearance of the ear-like 

 expansions in the latter is fully understood. The connection with 

 Steph. Herveyi and Steph. macrocephalum can also be traced quite 

 satisfactorily through the series described by Quenstedt, and also 

 studied by myself. 



Thus Steph. subcoronatum appears theoretically as the typical form 

 of the group, a result which was entirely unexpected, since, until this 

 summary was written, I had always pictured Humphriesianum proper 

 as the centre of affinities. Some of the specimens are inseparable 

 from Humphriesianum proper until the young are consulted. These 

 invariably show the typical Steph. subcoronatum or nodosum form and 

 characteristics very distinctly, and are also of a smaller size than the 

 corresponding Humphriesianum varieties. The peculiar broad abdo- 

 men which characterizes the adults of nodosum and the young of sub- 

 coronatum and Humphriesianum, I shall have frequent occasion to 

 speak of, and as its resemblance is general rather than special, I shall 

 speak of it usually as the Pettos-like form, in allusion to its ancestral 

 derivation. 



S. Blagdeni may be briefly described as a huge form of a young 

 sub-coronatum of the broad abdomened variety in some of its forms; 

 in others, however, the abdomen becomes elevated, and no line can be 

 drawn between these and the succeeding, or true Steph. coronatum 

 series. The peculiar broad abdomened forms which began to appear 

 in varieties of Steph. subcoronatum are in Blagdeni, the predominate 

 ones, and represent the species. The young changes but slightly by 



