108b YORKSHIRE TYPE AMMONITES— II June 



108. AMMONITES HEPTANGULARIS, Young & Bird 

 (Plates CVIIIa, b, c) 



Original Description 

 [Young & Bird, 1828, pp. 263, 359.] 



" No. 1, PI. XIV, is a very rare and singular shell, from the Hawsker 

 shore, armed with a double row of spines, placed on angular ridges on 

 the sides. Between the two rows are irregular ribs, running from the 

 inner knobs to the outer ; and each generally splits into two elevated 

 ribs on the back, partly fimbriated ; whereas on the inner part of the 

 whirl, within the interior row of knobs, the ribs are replaced by numerous 

 slender striae. The space between the rows is also slightly striated. 

 The whirls are few, the outer whirl being very large, and the central part 

 forming a deep cavity, or umbilicus : the inner whirls are much con- 

 cealed. The back is rounded, but seems to acquire an angle behind, 

 near the aperture ; which, therefore, approaches to heptangular. On 

 this account, we may name this species A. heptangularis." 



" [P- 359-] Plate XIV. fig. 1. Ammonites heptangularis. Lias 

 bands. 



Remarks 



Proportions : ( 98 47, 53, 20. 



I 162 47 46 27. Perplaty-, extremi-, to 

 perpachygyral, angustumbilicate. 



Stages, conch, subsphserocone ; periphery, 1 ; ornament, 5**. 



The specimen, which has nearly complete body chamber, is in poor 

 condition, with various displacements due to crushing. The angular 

 piece of matrix which Young & Bird depict as extending from the aperture 

 is seen on the right side of the specimen. On the same side is to be seen 

 evidence for the tubercles which they show in the umbilicus. 



Genus, Liparoceras, Hyatt ; family Liparoceratidae. Geological 

 position is, according to Simpson, who describes this specimen as 

 A. Henleyi, syn. A. heptangularis, diameter 7 inches (1855, 70 ; 1884, 

 105), M.L. x (1884, p. xviii) ; " this is from one of the beds which unite 

 the Middle with the Lower Lias at R. H. Bay " (1884, 105). M.L. % 

 seems too high. The specimen shows spotting like that of A. maculatus, 

 and therefore L.L. a — c may be suggested. 



Result 

 Liparoceras heptangulare, Young & Bird sp. 1828, Char- 

 mouthian, [striatum zone], Hawsker, near Whitby. 



