Hyatt.] 386 [June 7, 



every way than the adjoining whorls, but no signs of old age were 

 visible. The finest suites of this species occur at the Bristol Mu- 

 seum and in D'Orbigny's collection. 



One specimen in the latter shows an extremely long and complete 

 living chamber, occupying one and one quarter volutions. The 

 entire diameter of the specimen was 210 mm. The involution of 

 the whorls was noticeably decreasing at about 30 mm., and continued 

 steadily to decrease, accompanied by a corresponding diminution in 

 the size of the whorl until the difference in size and form at the 

 mouth became very marked. This specimen exhibited an extreme 

 variation, and should be more exactly, perhaps, associated with 

 nodosum. In other stouter and more normal forms the involution 

 decreases at a slower rate, and begins later in the life of the individ- 

 ual, and in some individuals it is not perceptible at all. It is evident 

 that either no absorption of the living chamber takes place, or only 

 a partial one took place during the growth, since the diminution in 

 the size of the living chamber simply continues that which occurs in 

 the body of the shells, where the sutures are well marked. This 

 may be noticed in any large collection of this species. A fragment 

 of the mouth of a specimen which must have attained a diameter of 

 at least 300 mm., still possessed the tubercles and shewed no signs of 

 old age beyond this decrease in diameter. In Dr. Wright's collection 

 a fine specimen (size not noted) exhibited the living chamber and 

 mouth complete; the last whorl was smooth for almost the entire 

 length, the tubercles and ribs small in the adult. 



SECOND SERIES. 



Stephanoceras subcoronatum. 



Amm. subcoronatus Oppel, Jahressch. Nat. Wurtt., Vol. 12, p. 496. 



Amm. coronatus-oolitlucus Quenst., Die Ceph., pi. 14, f. 4. 



Amm. Humphriesianus Sow., Min. Conch., pi. 500, fig. 1-2 (not 3). 



This species is distinguished from nodosum only by the greater 

 proportionate breadth and flatness of the abdomen, and the abrupt- 

 ness of the umbilical sides, continuous increase in the size of the 

 whorls by growth,. finer ribs, and so on. These characteristics may 

 be summed up in a few words as precisely intermediate between 

 nodosum and Blagdeni. The adults are smaller, but quite similar to 

 the latter, and though larger than the young of Humphriesianum, 

 almost identical with them in aspect externally, though probably 



