The familiar Dogfish are small, slender sharks possessing large numbers of very small clipping teeth, of equal size and form throughout the jaws.  Typically these are low and wide, labio-lingually flattened, with a triangular and strongly inclined (sub-horizontal), posteriorly directed  central main cusp, resting on a rounded accessory cusp.  A broad, rounded, pendant-like extension of the crown hangs down over the labial face of the root directly below the main cusp. 

Though they are rarely observed by the amateur collector, isolated teeth (Protosqualus) are often the commonest microscopic shark teeth in the Grey Chalk.

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1).  Protosqualus sigei- representative isolated Squaliform teeth from the Albian Gault Clay of Folkestone, David ward Collection: (A) x13; (B) x13.  Images by kind permission of David Ward.  See also www.gaultammonite.co.uk [Fossils of the Gault Clay]. 

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2).  Modern dogfish for illustration; (A) Spiny Dogfish (Squalus acanthias) (image sourced from ARKive, © Andy Murch / Elasmodiver.com); (B) Shortnose Spurdog (Squalus mitsukuri) (image sourced from ARKive, © Ron & Valerie Taylor / ardea.com).