AMALTHEUS. 



383 



tions on the mould. The body-chamber is long in the older forms, thus in Arcesfes it is 

 a whorl and a half, and in Amaltheus two thirds of a whorl in length. The mantle-impres- 

 sion in Arcestes has left deep constrictions around the aperture of the body-chamber, 

 which are absent from the polythalamous portion of the shell. 



Arcestes, Bidymites, Lobites, PtycJiites, Finacoceras and Sat/eceras, are obtained only 

 from the Trias ; Amaltheus from the Trias, Lias, and Jurassic rocks, and Scldoenbachia 

 is limited to the Cretaceous formation. 



Genus III. — Amaltheus. Montfort, 1808, 



Genus — Amaltheus, 

 Family — Amalthei, 



Amaltheen, 



Am ALT HE I, 



Montfort. Conchyliologie Systematique, t. i, p. 91, 1808. 



von Buck. Ueber A'mmoniten, Abb. Akad. Berlin, pp. 143, tab. 3, 



fig. 3, 1832. • 

 (T Orhigny . Paleontologie Frangaise Terr. Cretaces, t. i, p. 407, 1840, 

 Quenstedt. Cepbalopoden, p. 92, 1849. 

 Giebel. Fauna der Vorwelt, b. iii, p. 537, 1852. 

 Pictet. Traite de Paleontologie, 2nd ed., t. ii, p. 676, 1854. 



— Seehuch. Hannoversebe Jura, p. 139, 18G4. 



OxYNOTEN, Beyrich. Ueb. Cepbalopd. Musclielkallc. der Alpen, p. 136, 18G; 

 Genus — Pleukoceras, Hyatt. Bulletin Mus. Comp. Zool. Harvard Coll., p. 89, 1866. 

 Amaltheus, Hyatt. Ibid., p. 90, 1866. 



— Ilojsisovics. Jabrb. geol. Reichsanstalt, p. 580, 1869. 



— Waayen. Palseontograpbica, b. xvii, p. 201, 1870. 



This genus is characterised by having a compressed discoidal shell ; the siphonal area 

 narrow, sharp, and keeled ; the ribs when present are all flexed forward and end in a keel 

 or plaited ridge (fig. 190). The external shelly lamina in some species develops fine 

 longitudinal spiral lines. The body-chamber is short, about one half to two thirds of a 

 whorl. The mouth-border of the shell is simple, the ventral portion 

 ending in a long projecting process. The lobe-line is extremely com- 

 plicated and very difficult to trace. The siphonal lobe is shorter 

 than the principal lateral, which is mostly broad and wedge shaped. 



This genus presents three distinct types of shell form which 

 appeared together about the same period of time, they are therefore 

 not derived from each other, but descendants of different groups; 

 the first of these has Amaltheus Greenovghi and Amah Guibalianus, 

 the second Amaltheus oxynotus, and the third Amaltheus maryari- 

 tatus as their representatives. 



Dr. Waagen states that a horny divided Anaptychus has been found in some species. 



This genus has an extensive range in time. In the Trias is found Amal. meyalodiscus. 



Fig. 190.— Amaltheus cor- 

 datus. Sow. 



