etages,  cloud  genera,  cloud  species,  and  cloud  varieties used to identify clouds. To improve your understanding of the many cloud types, be sure to locate the specific classification of each cloud in table 1-1 during the following discussion. Cloud Variety In the 27 states-of-the-sky, many of the differences between  different  “cloud-states”  are  not  based  solely  on genera, but on a combination of the genera, species, and variety.   Cloud   variety   identifies   the   specific appearance of the arrangement of elements within a cloud layer, the thickness of the layer, or the presence of multiple layers. The nine different cloud varieties are used to further identify cloud species by specific appearance. The variety name is appended after the species name to further identify a cloud. An example is “stratus nebulosus opaqus,” which is a low-etage stratiform  cloud  (genus,  stratus)  without  distinct features (species, nebulosus) but dense enough to obscure the sun (variety, opaqus). State-of-the-sky codes usually do not name the cloud variety, but give a description of the dominant cloud genus, species, and variety. The nine varieties in table 1-1 are defined as follows: Opaqus: A sheet, layer, or patch of clouds the greater part of which is sufficiently dense to obscure the sun or moon. Opaqus is used to modify low- and mid-etage  stratiform  cloud  layers,  particularly  those of the species stratiformis. It is not used with the species cirrus spissatus, since spissatus is inherently opaque. Perlucidus:  Clouds  of  the  genus  alto-  or stratocumulus, usually of the species stratiformis, in which the distinct spaces between the cloud elements allow blue sky, the sun, moon, stars, or higher clouds to be clearly seen. Translucidus:  A sheet, layer, or patch of clouds the greater part of which is sufficiently translucent to reveal the position of the sun or moon. The term is used to modify low- and mid-etage stratiform cloud layers, particularly those of the species stratiformis. It is not used  with  any  of  the  high-etage  cloud  names,  since these clouds are inherently translucent. Duplicatus:  Two or more sheets, layers, or patches of cloud of similar type at different levels in the atmosphere,  commonly  overlapping.  This  situation  is usually associated with the species fibratus, uncinus, stratiformis,  and  lenticularis. Undulatus: Elements or cells in a sheet, layer, or patch of clouds arranged in parallel rows and forming a wavelike pattern similar to swell waves in the ocean. The popular names for these cloud patterns are "billow clouds,"  "wind  row  clouds,"  and  "wave  clouds."  This wavelike pattern is principally found in the genera cirrocumulus,  altocumulus,  altostratus,  and stratocumulus,  but  is  rarely  associated  with  stratus. When distinct rows and columns are apparent in the pattern of cloud elements in a single layer, the term bi- undulatus may be used. Radiatus: A cloud pattern, similar to undulatus, in which cloud elements in the rows are merged together so that parallel bands of clouds are formed. Due to the effect of perspective, these straight parallel bands seem to merge together near the horizon. The popular name for this cloud pattern is Abraham's Tree. This pattern is frequently   associated   with   the   genera   cirrus, altocumulus,  altostratus,  and  stratocumulus,  and usually associated with the species stratiformis. Lacunosus:  A  cloud  pattern  in  which  the rounded holes between the clouds form a honeycomb or netlike pattern is the dominant feature. The clouds may be equated to the wax of a honeycomb or the cord in a net.  This  pattern  is  associated  with  the  genera cirrocumulus and altocumulus, and is usually used to further define the species stratiformis, castellanus, or floccus. Intortus: Associated only with the genus cirrus, this term is used when the cirrus fibers or filaments are entangled, curved, bent and irregular, or form a zig-zag pattern. Vertebratus: Associated mainly with the genus cirrus, this term is used when the cloud fibers extend outward  from  an  elongated  central  core  and  are suggestive of vertebrae, ribs, or a fish skeleton. Supplementary Features Clouds may also be identified by the presence of supplementary  cloud  features.  Supplementary  cloud features are specific portions of a larger cloud. Most supplementary   features   are   associated   with cumulonimbus clouds. Virga, tuba (funnel clouds, tornadoes, waterspouts), incus (anvil tops), arcus (roll clouds),   wall   clouds,   mamma   (formerly   called mammatus),  pileus,  velum,  and  pannus  are  all supplementary  features  of  cumulonimbus  clouds. Virga may also be associated with many cumuliform clouds, and pannus with nimbostratus clouds. Cloud 1-8