ABSTRACT
Examples of many spinose brachiopod genera were studied and a consistent difference was found between the spines of siphonotretids and the Productida as compared to those of most Rhynchonelliformea. We describe these two forms of hollow spines as ‘tubular hollow’ and ‘sutured hollow’, and a model of growth for both types is suggested. Comments on other external spine-like outgrowths developed by some Rhynchonelliformea are also made.
