A new reconstruction of the skull of Crassigyrinus scoticus (Lydekker) is provided, based on newly prepared material. A revised interpretation of the naris shows it in most respects to be like that of other Carboniferous tetrapods, lacking both an anterior tectal and a lateral rostral. However it does incorporate an enlarged septomaxilla, and part of the dorsal surface of the vomer is also visible within the naris of most specimens. Prominent paired buttresses run along the midline of the snout, and a single bowl-shaped interpremaxillary fenestra pierces the snout and palate but is not confluent with the naris or choana. A preopercular is probably absent. A new cladistic analysis places Crassigyrinus with the Viséan genus Whatcheeria, and puts those two taxa as a sister-clade to the anthracosaurs Proterogyrinus and Pholiderpeton. Temnospondyls form a clade with loxommatids, and these two arms form a dichotomy crownward to Greererpeton, Ichthyostega and Acanthostega which are successive stemward plesions.
