Extract
One of the problems left unsolved in my “Revision of the Jurassic Cephalopod Fauna of Kachh” consisted of the determination of the exact age of certain Jurassic beds that had yielded (in addition to ammonites) species of Trigonia. Among these, T. smeei J. de C. Sowerby is of unusual, general interest; and, as readers of the Geological Magazine may remember, this species has been the subject of much controversy. It was one of the species whose “morphological position, viewed from the evolutionary standpoint”, caused them to be described as Cretaceous. Thanks to the continued researches of Mr. J. H. Smith, of Bhuj, who has been good enough to send me new collections from various critical sections in Kachh, I am now in a position to add to the evidence for a Jurassic age of a number of these species of Trigonia. If it be asked why, in a work on cephalopods, I have gone out of my way to express scepticism regarding the use of species of Trigonia for correlation, I can only say that this genus happened to be represented among the ammonite material sent to me. There is no reason, so far as I can see, why Trigonia should not be quite as useful for zonal purposes as ammonites. I have been equally sceptical about Stolley’s work on belemnites. But in either case I will leave the results to speak for themselves. It seems to me that if Upper Oxfordian species like Trigonia smeei and such allies as T. tenuis, T. tra-peziformis, T. remota Kitchin, not to mention the associated Astarte, Gervillia, Cucullaea, Exogyra, etc., could be claimed to be of Cretaceous age by one of the most eminent authorities, then it is time to remind the general palaeontologist again of what workers on ammonites have realized long ago.