British Grammysiidae (bivalvia).

A study of the British members of the family Grammysiidae S.A Miller 1877 has been undertaken. Most of the taxa are Silurian in age; others are, rarely, Upper Ordovician or Devonian in origin. One species found derived in Triassic strata is included and its origin traced. Wherever possible, existing type material has been located and a primary revision made. This work has been augmented by studies on new and existing collections. The diagnosis of the family has nov been restricted to include only those members of the Superfamily Pholadomyacea vhich show the characteristic Grammysiid cincture (fold and/or ribs) crossing the shell from the umbo to the ventral margin to there cause a folding of the shell. The type genus Grammysia De Verneuil 1847 is redescribed; its type species and type specimen designated and described. Numerical taxonomy has been used extensively and each species' description is accompanied by a table(s) of measurements. Three new genera and several new species are described. One chapter is devoted to computer applications in the study of Grammysiid bivalve systernatics, evolution and ontogeny. It includes sections on cluster analysis and discriminant analysis and evaluates the uses of these techniques in the various branches of 'palaeontology'. The section on palaeoecology gives a detailed discussion of the mode of life end habitat of each of the 19 species described in the section on systematic palaeontology. It discusses the functional significauce of the Grammysiid cincture and illustrates the Grammysiidae in their life positions and habitats at several periods from Ashgillian to Devonian times. The importance of environment to evolution is discussed. A summary of the evolution of the Grammysiidae is included. A new technique for coating fossils prior to photography is described.