Phymosoma maastrichtensis spec. nov., a fossil echinoid from the Cretaceous of Maastricht (Echinacea, Phymosomatoida, Phymosomatidae)

A beautifully preserved fragment of the test of a fossil Echinoid from the Maestrichtian Cretaceous, found at Belvédère, Caberg and kept in the Natuurhistorisch Museum, Maastricht under no. 1340, differs from the other species of the genus Phymosoma, hitherto described (cf. Fell & Pawson, 1966: U 395). It is a great pleasure to dedicate the description of this obviously new species to my friend and colleague Leo Brongersma in remembrance of the many and wide contacts we enjoyed since I tried and initiated him into the secrets of zoological museumwork, while as a student he occupied an ever increasing space in my room at the Zoological Museum of Amsterdam University. The fragment of this Phymosoma includes an ambulacrum and an interambulacrum and remnants of the adjacent ones. It is complete adorally, but incomplete near the apex. The height of the test must have been about 13 mm. The mouth is slightly but distinctly sunken. The ambulacrum is at the ambitus about 7 mm wide, the interambulacrum about 10.5 mm. A reconstruction of the ambitus circumference gives a horizontal diameter of 23 mm and a peristome of 12.5 mm diameter, while the periproct may also have been of about that size. In the ambulacrum a row of 14 tubercles is present, in the interambulacrum 12 tubercles. There must have been some more, as may be deduced from the size of the tubercles near the top of the fragment, as well as from the fact that at this adapical end of the test fragment the ambulacrum is 4 mm wide and the interambulacrum 61/2 mm, while at the peristome the A is 31/2 mm wide, the I A 4 mm. The tubercles are imperforate and in two of them distinct traces of the crenulation were detected. In the interambulacrum two distinct rows of primary tubercles are seen,