AMMOXOIDEA. 



36 3 



of the last volution. The external side of the shell is acute, or is 

 provided with a projecting keel, which is often hollow. The sutures 

 are usually deeply incised, but may resemble those of Ceratites in 

 form. A horny " Anaptychus ? ' has been shown to exist in a 

 number of forms. 



The type-genus of this family is Amaltheus itself, in which the 

 shell figs. -, ; _. 785 is furnished along its external margin with an 



Jtf^^jHl; 



Ammonites) mar- 



± :z 785 — AmaUAei 1 Am untites) 



Jurassic ^Coral Rag). 



acute or transversely plaited kee". The surface may be smooth, 

 striated, or transversely ribbed. The aperture is furnished with a 

 ventral process, and the sutures have deeply incised lobes and 

 saddles. Xumercu- 5] e rs of this genus are found in the Jurassic 

 re :':-. beginning in the lias. 



Nearly allied to the preceding is the genus Schloenbachia (figs. 

 7S6. 7S7), in which the external side is broad, and is furnished 

 with a strong median 

 keel, in the hollow of 

 which the thick siph- 

 uncle is usually con- 

 tained. The surface is 

 transversely ribbed, and 

 the aperture is falciform, 

 and is provided on its 

 ventral side with a for- 

 wardly directed process. 

 The species of this genus 

 are exclusively Cretace- 



- and range from the 

 Xeocomian to the Chalk. 



In the Cretaceous 

 genus Buch the external edge of the shell is acute or keeled, 



but the sutures resemble those of Ceratites so closely that the 

 forms of this type were formerly referred to the latter. Lastly, 



- - — Tlnd-view 

 of Schloenbachia cris- 

 ."retaceous. 



