多鳃鱼类一新属及该类鱼感觉沟系统的变异

本文记述了云南曲靖早泥盆世翠峰山组西山村段多鳃鱼类一新属种,变异坝鱼(Damaspis vartus gen.et sp.nov.)文中讨论了多鳃鱼类头甲背部感觉沟系统的基本模式,它的变化和变异。从这个基本模式出发笔者认为三岔鱼科和多鳃鱼科有许多重要的特征相近,似乎应把三岔鱼科和多鳃鱼科隶属于同一个高一级的分类单元即多鳃鱼目,而不应把三岔鱼科置于“华南鱼目”。“华南鱼目”是根据了解还不多的华南鱼属建立的,有些勉强,建议暂不采用。文中首次指出多鳃鱼类的感觉沟系统存在变异现象并认为在确立新类型时,变异是应该考虑的一个重要因素。

A NEW AGNATHA AND ITS SENSORY SYSTEMATIC VARIATION

A new form of Polybranchiaspids, Agnatha, Damaspis vartus gen. et sp. nov., was collected from the lower part of Cuifengshan formation (lower Devonian), Qujing district, Yunnan province. The diagnosis of the new genus and type species is as follows: Head and anterior part of body covered by a cephalic shield, postero-dorsal margin of which with a less convex dorsal spine; Postro-lateral margins of the shield with two developed pectoral corners; Ends of the corners placed more latterly than the end of the spine, with a little distance between two pectoral corners;Naso-hypophysial depression, transversal and ellipse-like in form, with a level posterior margin, situated on the anterior dorsal side of the shield; Orbital openings, longitudinal and ellipse-like in form, medium-sized, placed near rostro-lateral margin of carapace, behind the nasohypophysial depression; Sensory system displaying Polybranchiaspoid pattern, but longitudinal lateral canal prolonging backward into the pectoral corners, transversal lateral canal with dichotomous ends consisted of 4 longer canals and 3 other shorter ones; Having 15 branchiale sacs in each side. REMARKS The new Polybranchiaspid differs much from Polybranchiaspis in develloped pectoral corners, relation between the corners and the spine, canals with the dichotomous ends and more numerous branehiale sacs. It differs greatly from Laxaspis in having a less convex dorsal spine, a little distance between two pectoral corners, the longitudinal lateral canals prolonging backward into the pectoral corners and transversal canals with the dichotomous ends. Therefore the materials dealt with in this paper are named by the authors as a new form Damaspis vartus gen. et sp. nov., Damaspis means the fossil locality is near a dam, wartus shows the variation of the sensory system in Damaspis. DISCUSSION The sensory system pattern on the carapace in Polybranchiaspiformes is very stable. This pattern shows the supraorbital systems, the infraorbital systems and a median dorsal commussure; The supraorbital systems includs V-shaped pineal canals which do not contact immediately with the median dorsal commussure. On the basis of the Pattern there are some changes which belong to the family, generic or specific ones, eg. a short longitudial canal connect the pineal canals and the median dorsal commussure in Sanchaspidac. There are also some variations in the sensory system besides the normal changes, eg. Damaspis does not have symmetrical canals on the left and right sides of the shield. There are many close resemblances between the families Sanchaspidae and Polybranchiaspidae, though the shapes of their shields are very different: The sensory system of Sanchaspidae on the shield must also belong to Polybranchiaspoid pattern ; With regard to the forms and position of the naso-hypophysial depression, orbital openings and pineal, Sanchaspidae is very similar to Polybranchiaspidae. To our surprise, two typical genera, Polybranchiaspis and Sanehaspis, have similar oralo-branchial cavity and almost equal nomber of the branchial sacs; Their ventral portion of the interzonal part is not complete and leaves a similar median gap in the exoskeleton. According to the aforesaid fact, the authous believe that Sanchaspidae should be put in a same order with Polybranchiaspidae——Polybranchiaspiformes and can not be placed in "Huananaspiformes." "Huananaspiformes" was established by Janvire 1975 according to Huananaspidae Liu that included only one genus and one species, Huananaspis wudinensis Liu. At that time and even today, our knowledge of Huananaspis has been confined to the shape of the carapace, the naso-hypophysial depression and orbital openings. Thereforethe authors believe that there is not sufficient reason for establishing a new order according to a few exterior characters of Huananaspidae.