Page:VCH Lancaster 1.djvu/81

PALÆONTOLOGY stegocephalian amphibians known as Microsauri. It was described by Dr. A. Smith Woodward in the Geological Magazine for 1891 (p. 211), and belongs to a genus of which the first known specimens were collected by the late Sir William Dawson from hollow Lepidodendron trunks in the Nova Scotian Coal Measures. Of that genus it is the only known British representative.

The second and more typical Lancashire labyrinthodont, which was obtained by Mr. Wild in the Middle Coal Measures of the Bardsley Colliery, is at present undescribed. It is regarded by Mr. Bolton as probably referable to the Carboniferous and Permian genus Archegosaurus.

Passing on to the Coal Measure fishes, and commencing with those primitive Palæozoic sharks known as Ichthyotomi, the first specimen to record is a spine from the Lower Foot Mine at Littleborough, identified by Mr. Wellburn with Pleuracanthus cylindricus, a species known elsewhere from the Coal Measures of Scotland, Northumberland, Yorkshire, and Staffordshire. Mr. Bolton includes in his lists P. lævissimus, P. undulatus, P. erectus, and P. denticulatus; the first of these is a good species, but the second is a synonym of the first, and the other two are founded on spines. The allied genus Diplodus is represented in the county by two species, D. gibbosus and D. tenuis, of which the first alone is recorded from Littleborough; D. tenuis has a distribution very similar to that of Pleuracanthus cyclindricus, but D. gibbosus is not known to occur in Scotland. Among the more typical sharks, the Palæozoic family of Petalodontidae, characterized among other features by the pavement-like dentition of a peculiar type, is represented by several species in the Carboniferous of the county. Firstly, we have Ctenoptychius apicalis, typically from Staffordshire, recorded by Dr. Smith Woodward as a Lancashire fish; while Mr. Bolton mentions a second species, C. lobatus, typically from Scotland. Mr. Wellburn includes in his Littleborough list a member of another genus, Callopristodus pectinatus, first described from the Scottish coal-fields. To another family of Palæozoic sharks, the Cochliodontidæ, whose nearest relationships are probably with the Port Jackson sharks (Cestraciontidæ), belongs Pleuroplax rankini, of which remains are recorded from Littleborough, the species having a wide distribution in Britain. The Northumberland species P. attheyi appears in Mr. Bolton's list. Next on our list comes a species of the genus Sphenacanthus (belonging to the family Cestraciontidæ), which Mr. Wellburn considered might be new; it is represented by a spine from the Lower Foot Mine of the Littleborough district, said to be unlike any hitherto described. Mr. Bolton's Lancashire list includes, however, only the widely distributed S. hybodoides. Certain other specimens from the Littleborough district are of the type of those to which the ill-defined name Stemmatodus has been applied, such specimens being probably dermal ossifications belonging to Pleuracanthus or one of the allied genera. The imperfectly-known genus Tristychius or Petrodus is represented in the Yoredale rocks near Todmorden. A single spine from the Littleborough district is assigned to Acanthodes wardi, a species typically from Staffordshire belonging to an altogether peculiar group of Palæozoic sharks collectively known as Acanthodii; remains of the same genus are recorded by Mr. Morton from St. Helens, and the species occurs in Mr. Bolton's list. Following this come two representatives of the lung-fishes, or Dipnoi, belonging to the extinct genus Ctenodus, which takes its name from the somewhat 33