4ib YORKSHIRE TYPE AMMONITES Nov. 



41. AMMONITES COMPACTILIS, Simpson 

 (Plates XLIa,b) 



Original Description 

 " 119. A[mmonites] compactilis. [M. Simpson, 1855, p. 75.] 



[" II. With a keel on the back. 

 " a. Outer whorl broad." p. 72.] 



" Much depressed ; inner volutions nearly concealed, outer whorl 

 more than J the diameter ; radii waving, nearly obsolete ; obsoletely 

 striated ; keel rounded, entire ; aperture acutely triangular, or ovate ; 

 diameter ij inch. 



" This, Hke Boulbiensis, and the next [A. lectus, Simp.] has the keel 

 formed by a slight groove on either side, and some specimens have a 

 faint rim round the small umbilicus ; but it is a much more depressed 

 and elegant species than A. Boulbiensis. The foliations of the septa 

 are also very different, being far more delicate and numerous, crowding 

 the whole surface with their ramifications ; one set of lobes touching, 

 or nearly touching one another. I can count six principal lobes between 

 the keel and the inner margin of the whorl." 



Additional Details 



Simpson, 1884, no, adds to end of first par. " U.L., 7." 



Remarks 



Stages, conch, oxycone ; periphery, 3c, concavifastigate ; orna- 

 ment, 3c. 



The slight groove on either side of the keel is presumably the relic 

 of a furrow such as that shewn by A. suhconcavus, No. 10. 



It is not certain that the specimen (PI. XLIa) is the type ; but it 

 agrees with Simpson's description and measurement. It may be the 

 type from its history : it belonged to Dr. Lycett, and bears his label, 

 thus : " This is the A. compactilis of Simpson. It approaches Lythensis, 

 but as it comes from a different bed, has different sutures, and the outer 

 whorl always entirely overlaps the inner, I consider it a species." 



Genus, Pseiidolioceras, S. Buckman, 1889 ; family Hildoceratidae. 

 Geological position, Simpson says U.L. 7 ( = Jet Rock) ; Blake, 1876, 

 309, gives " zone of A. jurensis." 



Result 



PsEUDOLiocERAS COMPACTILE, SiMPSON sp. 1855, Yeovilian {stria- 

 tulum zone, Peak], Robin Hood's Bay, near Whitby. 



