The forms which Mr. Davidson in his invaluable Monograph has included under T. ovoides, are so various that it would be possible to refer the shells figured in the plate to that species, but since T. trilineata, from the Inferior Oolite, and T. lata and T. ovoides, from drift-blocks—which I shall endeavour to show are of the very latest Jurassic horizon—are very different in many respects, I prefer to give a new name to this form, which may find its place near T. ovoides and T. simplex. The specimen drawn, Fig. 1 and la, is from the collection of Mr. Roper of Lowestoft, who obtained it, with another specimen, from a gravel-pit at Thorpe in Suffolk. It has the general simple form of T. ovoides, but is remarkable for its great size. The imperforate valve is flattened in the mesial line, whilst the perforate valve is deep and raised into a well-pronounced keel in the mesial line extending from the beak; the foramen is small. The specimen figured is longer than the other in Mr. Roper's collection, which has the shorter, squarer form of Fig. 2, resembling T. simplex. This fine Terebratula may be known as T. rex.