Mitchell, S.F. 2013. A new rudist bivalve Curtocaprina clabaughikinsorum gen. et sp. nov. from the Middle Albian of Texas and its bearing on the origin of the Ichthyosarcolitidae Douvillé. Caribbean Journal of Earth Science, 45, 85-89. © Geological Society of Jamaica. Available online 21 st May 2013. 85 A new rudist bivalve Curtocaprina clabaughikinsorum gen. et sp. nov. from the Middle Albian of Texas and its bearing on the origin of the Ichthyosarcolitidae Douvillé SIMON F. MITCHELL Department of Geography and Geology, The University of the West Indies, Mona, Kingston 7, Jamaica Email: barrettia2000@yahoo.co.uk ABSTRACT. A new rudist bivalve, Curtocaprina clabaughikinsorum gen. et sp. nov. is described from the Middle Albian of Texas. This species shows characters that relate it both to the Caprinuloideidae and to the Ichthyosarcolitidae. It shows a small posterior tooth separated from the large anterior tooth by a central socket as well as an additional toothlet (called here the ichthyosarcolitid toothlet) and two plate-like myophores in the left valve. The anterior tooth and ichthyosarcolitid toothlet fit into slots in the body chamber of the right valve, whereas the two wall-like myophores face directly onto the inner surface of the body cavity in the right valve. Curtocaprina is a primitive member of the Ichthyosarcolitidae and suggests that the family originated before the mid Albian most likely from an as yet unknown primitive form of Caprinuloideidae. Key words: Rudist bivalves, Cretaceous, Albian, Curtocaprina new genus, Ichthyosarcolites, Texas. 1. INTRODUCTION The Ichthyosarcolitidae Douvillé, 1887, is an enigmatic family of rudist bivalves which does not fit easily into cladistic analyses (e.g., Skelton and Smith, 2000). New light was shed on their origin at the Eighth International Congress on Rudist Bivalves in Izmir, Turkey, in 2008, when Javier Aguilar Pérez (Aguilar et al., 2008) discussed the myocardinal arrangement of Mexicaprina alata Filkorn, 2002, and suggested that this species belonged to Ichthyosarcolites and not Mexicaprina, a sentiment with which I agree. In 2009, I spent a month studying the collections of the Texas Memorial Museum, and during this study I came across a few specimens of a small canal-bearing rudist from the Edwards Limestone of Texas. It is these specimens that are described here and shed new light on the origin of the Ichthyosarcolitidae. 2. AGE AND DERIVATION OF MATERIAL The specimens in the Texas Memorial Museum were collected by S. E. Clabaugh and W. C. Ikins in Bush-Whack Creek, 10 miles (16 km) SW of Kerrville, Kerr County, Texas, during their study of the Edwards Limestone (Ikins and Clabaugh, 1940). The specimens are indicated to have been derived from a level about 50 ft. (15 m) above the base of the massive limestone of the Edwards Formation, on the crest of a low hill on the fence line between the Allen and Strohacker ranches, about ½ a mile (0.8 km) southwest of the Allen Ranch House (Ikins and Clabaugh, 1940). The fauna is silicified and weathers out of the Edwards Limestone. Mancini and Scott (2006) correlate the Edwards Limestone with the interval from the mid Middle Albian to the earliest Upper Albian, and since the specimens come from the lower part of the Edwards Limestone a mid to late Middle Albian age seems appropriate. 3. SYSTEMATIC PALEONTOLOGY The classification adopted here follows Skelton (2011) and Carter et al. (2011), as modified by Skelton (2013 this volume). Specimens are preserved in the collections of the Texas Memorial Museum, University of Texas at Austin, Texas (TMM numbers); comparative material of Ichthyosarcolites Desmarest is housed in the Museum of Paleontology, Institute of Geology, Universidad Nacional Autónoma de México, Ciudad Uiversitaria, México (IGM numbers). ORDER HIPPURITIDA Newell, 1965 SUBORDER RADIOLITIDINA Skelton, 2013 SUPERFAMILY CAPRINOIDEA d’Orbigny, 1847 FAMILY ICHTHYOSARCOLITIDAE Douvillé, 1887 Diagnosis. Caprinoidea lacking an external ligamental groove, bearing an anterior tooth and an ichthyosarcolitid toothlet (see below) in the left valve that fit into slots in the right valve, and a central tooth in the right valve that fits into a socket in the left valve. The posterior tooth is reduced or absent. The myophoral plates in the left valve are rotated to face directly onto the inside wall of the body cavity in the right valve.