PLATE XXVIII. 



Zone of Aegoceras armatum. 



Fig. 1. Aegoceras armatum, Sowerby. Side view, natural size. A very fine type 



specimen. Leckenby collection. Wood- 

 wardian Museum, Cambridge. 



2. — — — Front view, showing the ribs and spines in 



profile. 



3. — — — Smaller specimen in same collection. 



4. — — — Siphonal area, showing spines of the left side 



absent. 



5. — — — Another specimen, showing spines of the left 



side truncated. My collection. 



6. — — — A very accurate tracing from another specimen 



of the highly complicated lobe-line, showing 

 the large size of the siphonal and principal 

 lateral lobes. My collection. 



