those of Spondylus marked with number 1, with photos of the holotype, preserved in Geneva, taken from different angles, and published by Finet and Lamprell in the book "The Spondylidae" in the historical collections of the Museum d'Histoire Naturelle,Geneva".The holotype is also depicted in Lamprell's book.In my opinion,the specimens shown in the photos are almost identical: the same irregular rough appearance in the left valve, the same remarkable depth of the right valve, the same sculpture on both valves, the presence of denticulation, clearly visible, as I said, even in the holotype, the same color.
COMPARISONS: Spondylus excavatus has been compared (and confused) with 2 species of the Mediterranean-Atlantic province, Spondylus gaederopus e Spondylus senegalensis.Spondylus excavatus, in my opinion, differs from Sp gaederopus as the latter is almost equivalve, has a different number of ribs,different spines and interstices. The color,too, is very different.Le two species also differ in the area of ??attachment  and the strong denticulation at the hinge, absent in Sp gaederopus.
As for differences with Spondylus senegalensis, while taking into account the variability of this species,it is almost equivalve (indeed, often the left valve is slightly convex, larger than the right), the strong denticulation at the hinge is absent and there's  a constant different ratio height of the shell-distance between the auricles;moreover, the shell of Spondylus senegalensis is more regular and orderly in the ribs, the interstices are not nodulose, the spines are, on average, longer and more
regular in outline.

I would welcome any comments from other collectors.

Dr. Michele Dardano   
Via Petrarca 43 71122
Foggia  (Italy)

Literature cited

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Internet Hawaiian Shell News     Page 2    June 2012     Feature 1