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H. L. Clark (1908) described S. pallidus from three small specimens collected from Sagami Bay, Japan. His description indicates they were little more than about half the size (TL=49 mm) of the holotype of S. lutkeni. Later (1917) he suggested S. pallidus might represent a young form of S. lutkeni. The differences he maintained separated the two species were the lighter colour and strongly keeled sternum of S. pallidus. Mortensen (1951), not having seen material of either species, was not able to clarify the relationship between them. Of the new material we have examined, the smaller specimens (TL up to 82 mm) are mostly broken, or at least aborally complete but orally incomplete. However, comparisons with three specimens identified by H. L. Clark as S. lutkeni and housed in the National Museum of Natural History, Washington, lead us to conclude that S. pallidus and S, lutkeni are conspecific. Specimens NMNH E4757 are juveniles, TL = 31 and 35 mm, with a relatively strong sternal keel. Specimen NMNH E791 measures TL = 65 mm, with a less pronounced sternal keel. Aborally these specimens compare well with our new material. The only detectable difference was in the primary tubercles of the new specimens, which like those of the holotype of S. pallidus (H. L. Clark 1971, pl. 157, fig. 1) are a little smaller. We believe this to be an acceptable range of variation. Interestingly, F. J. Fell (personal communication) found only the holotype of S. pallidus to represent that species, the paratypes being referable to S. paucituberculatus Agassiz and Clark. He similarly and independently concludes that S, pallidus and S. lutkeni are conspecific.

Mortensen, T. (1951). A Monograph of the Echinoidea. V, 2. Spatangoida II. Amphisternata II. Spatangidæ, Loveniidæ, Pericosmidæ, Schizasteridæ, Brissidæ, 593 pp., C. A. Reitzel, Copenhagen.  

Baker, A. N. & Rowe, F. W. E. 1990. Atelostomatid sea urchins from Australian and New Zealand waters (Echinoidea: Cassiduloida, Holasteroida, Spatangoida, Neoplampadoida). Invertebrate Taxonomy 4, 281-316. Available for editors  

Clark, H. L. 1917. Hawaiian and other Pacific Echini. Memoirs of the Museum of Comparative Zoology, Harvard College, 46, 85-283. available online at https://www.biodiversitylibrary.org/page/30650182