23b YORKSHIRE TYPE AMMONITES Mar. 



NAUTILUS SUBCARINATUS, Young & Bird 

 (Plate XXIII) 



Original Description 

 [Young & Bird, 1822, p. 255.] 



" Fig. 7, PI. XII, represents a rare and handsome umbilicated nautilus, 

 also from the alum shale. It is distinguished by a flat space running 

 along the back, divided in the middle by a slight ridge, or imperfect 

 keel. The sides are marked with fine striae, and with irregular undula- 

 tions ; and the edges of the septa, where exposed, are beautifully foliated. 

 This species is not so flat as n. Whitbiensis, nor so globose as n. pompilius, 

 and is much smaller than either. N. lineatus of Sowerby, Tab. 41, 

 resembles it, but is obviously another species. From its imperfect keel, 

 we may designate our shell «. subcarinatus." 



Additional Details 



Young & Bird, 1828, p. 271.— At beginning " Fig. 9 " for " fig 7 " ; 

 towards end of par. " N. astacoides " for " N. pompilius " ; omit sentence 

 about N. lineatus ; add at end of par. " The siphuncle, as in keeled 

 ammonites, runs under the keel." 



Remarks 



Stages, conch, sphaerocone ; periphery, 4 ; ornament, 3, or 3c. 



Genus Frechiella, Prinz, 1904, p. 31. Family Arietida2 ? 



The generic adventures of this species have been — .Nautilus ; Young 

 & Bird, 1822, 1828 ; Ammonites ; Phillips, 1829, Oppel, 1862 ; Phyllo- 

 ceras ; Blake, 1876 ; Wright, 1884 ; Harpoceras ; Taramelli, 1880 ; 

 Pelecoceras ; Haug, 1887; Poecilomorphus ; Bonarelh, 1893; Bellini, 

 1900 ; Cymbites ; Buckman 1894 ; Frechiella, Prinz, 1904 ; Parisch 

 & Viale, 1906. An allied species, A.sternalis, was made type of his genus 

 Paroniceras by Bonarelli, 1893. 



Though the present species may now be placed as Frechiella, of 

 which a Yorkshire specimen is the type, yet it may be doubted if the 

 species is any more than a Cymbites which shews anagenetic development 

 of a rounded periphery (i) into a carinate-sulcate (4). This would not 

 be a generic character, unless unmodified species of Cymbites continued 

 to co-exist : it is only a normal developmental phase (S. Buckman, 

 G. Mag. 1894 (4) I, 360). 



Result 



Frechiella subcarinata, Young & Bird sp. 1822, Whitbian, 

 subcarinatum zone [near Whitby]. 



