Solenochilus
Introduction '''''Solenochilus''''', type genus of the Solenochilidae is an extinct cosmopotilian nautilid from the Lower Pennsylvanian to the Lower Permian with a rapidly expanding, coiled globular shell with few whorls, from which prominent spines  extend laterally from the umbilical area at maturity. ''Solenochilus'' is derived from the Upper Mississippian ''Acanthonautilus'', principally through evolutionary changes in the siphuncle.The siphuncle in both ''Solenochilus'' and ''Acanthonautilus'' is ventral, running just inside the outer rim of the shell. In both the siphuncle is mostly composed of thin connecting rings. The siphuncle in ''Solenochilus'' is wider and has a more sinuous profile than that of ''Acanthonautilus''. Both swing dorsally between septa, but more so in ''Solenochilus''. In both the septal necks are somewhat long and straight on the ventral side but in ''Solenochilus'' they are cyrtochoanitic and recumbent on the dorsal side, rather than simply curved back, cyrtochoanitic. ''Solenochilus'' resembles its predecessor, ''Acanthonautilus''', in overall anatomy, and both genera superficially resemble ''Permonautilus'' from the Clydonautilaceae.
References * Kummel, B. 1964; Nautiloidea—Nautilida, Treatise on Invertebrate Paleontology, Part K, Nautiliodea; Geological Society of America and University of Kansas press