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butalso some significant differences that may imply that shell-carrying in thedromiids has evolved more than once. We provide a summary of relevantmorphological evidence and a hypothesis about the evolution of camouflagein dromiid crabs. The morphological and behavioural characters will need tobe eventually mapped on to a molecular phylogeny.Specimens that were used for this study came from the Western AustraliaMuseum (WAM), Queensland Museum, Brisbane (QM) and the Allan Han-cock Collection, now held by the LA County Museum, Los Angeles (AHF).The following abbreviations are used: CW is maximum carapace width, CL iscarapace length (dimensions given as CW × CL); P1 is the cheliped, P2–P3are the walking legs and P4–P5 are the shell-carrying legs; G1 and G2 are thefirst and second male gonopods. Live

We describe a new species of pygocephalomorph eumalacostracan from the Leitchfield Formation, Mississippian (Lower Carboniferous) of Kentucky, U.S.A. The fossils display a well-developed cephalothorax, pleon, and tail fan, and they show greatest affinity with other species within Tealliocarididae, especially to species of Pseudotealliocaris. The new species, Pseudotealliocaris holthuisi, is a second taxon of tealliocarid from the American Lower Carboniferous, the other being P. palinscari from the Mississippian of Pennsylvania. We compare the new species to other known species in the family and provide an overview of pygocephalomorph evolution.

[Les fossiles paleozoiques recemment decouverts ont elargi nos connaissances sur l'histoire du super-ordre des Hoplocarida. Cette comprehension plus etendue accentue que les hoplocarides sont uniques et suggere qu'ils derivent independamment des leptostracees, separement et distinctement des eumalacostracees caridoides. L'auteur presente des raisonnements pour et contre l'origine multiple des eumalacostracees, avec une exposition abregee des interpretations polyphyletiques et mono-phyletiques de l'histoire eumalacostraceenne telle qu'on la comprend actuellement., Les fossiles paleozoiques recemment decouverts ont elargi nos connaissances sur l'histoire du super-ordre des Hoplocarida. Cette comprehension plus etendue accentue que les hoplocarides sont uniques et suggere qu'ils derivent independamment des leptostracees, separement et distinctement des eumalacostracees caridoides. L'auteur presente des raisonnements pour et contre l'origine multiple des eumalacostracees, avec une exposition abregee des interpretations polyphyletiques et mono-phyletiques de l'histoire eumalacostraceenne telle qu'on la comprend actuellement.]

Siewing (1963) suggested that hoplocarids occupy an unusual phylogenetic position within the Eumalacostraca in that they have lost the first abdominal segment. In most other eumalacostracans the pretelsonic abdominal segment was lost from the original phylocaridan-type abdomen of seven segments. The major argument presented supporting a loss of the first abdominal segment in the Hoplocarida is the presence of an extra pair of lateral arteries in the first abdominal segment. The usual condition is one pair of lateral vessels per segment. Accounts of the circulatory system of adult stomatopods appear to concern only the genus S quilla (see Komai & Tung, 1931 ; Mayrat, 1958). My observations on the circulatory system of Hemisquilla ensigera (Owen) (see Stephenson, 1967) have shown significant differences from S quilla on the disposition of the lateral vessels.