Chidleyenoceras

Chidleyenoceras is a Middle Ordovician tarphyceroid with a closely coiled, evolute shell; whorl section subquadrate, widest just above a broadly rounded venter; dorsum with a broad shallow impression; sutures moderately spaced, weakly sinuous; siphuncle large, subventral, apparently orthochoantitic^{[clarification needed]} with tubular segments.

Chidleyenoceras Temporal range: Middle Ordovician
Scientific classification
Kingdom:	Animalia
Phylum:	Mollusca
Class:	Cephalopoda
Subclass:	Nautiloidea
Order:	Tarphycerida
Suborder:	Barrandeocerina
Family:	Plectoceratidae
Genus:	Chidleyenoceras Shimizu & Obata, 1935

The tubular, subventral siphuncle separates Chidleyenoceras from the Apsidoceratidae (Sweet, 1964) where it had been included and puts it well into the Plectoceratidae (Flower, 1984).