Holconautilus is a Nautiloid genus from the family Tainoceratidae

Tainoceratidae

The Tainoceratidae is a family of late Paleozoic and Triassic nautiloids that are a part of the order Nautilida, characterized by large, generally evolute shells with quadrate to rectangular whorl sections...

 and order Nautilida

Nautilida

The Nautilida constitute a large and diverse order of generally coiled nautiloid cephalopods that began in the mid Paleozoic and continues to the present with a single family, the Nautilidae which includes two genera, Nautilus and Allonautilus, with six species...

, named by Mojsisovics, 1902, and known from Upper Triassic

Triassic

The Triassic is a geologic period and system that extends from about 250 to 200 Mya . As the first period of the Mesozoic Era, the Triassic follows the Permian and is followed by the Jurassic. Both the start and end of the Triassic are marked by major extinction events...

 sediments in Europe

Europe

Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...

 and E Indies (Timor

Timor

Timor is an island at the southern end of Maritime Southeast Asia, north of the Timor Sea. It is divided between the independent state of East Timor, and West Timor, belonging to the Indonesian province of East Nusa Tenggara. The island's surface is 30,777 square kilometres...

). Its shell, evolute, discoidal, with simple coarse lateral ribbing; whorl section, subrectagular with a broadly arched venter.

Holconautilus somewhat resembles the Permo-Triassic Pleuronautilus

Pleuronautilus

Pleuronautilus is a Nautiloid genus; family Tainoceratidae, order Nautilida. The shell is evolute, discoidal; whorl section subquadrade, flanks generally straight but may converge toward the venter. Inner flanks have course ribbing, outer have rows of nodes. Sutures have shallow ventral,...

except its suture has ventral saddles instead of ventral lobes and lateral ribs are continuous. Anoploceras

Anoploceras

Anoploceras is a Middle and Upper Triassic nautiloid included in the Tainoceratidae, known from eastern Europe. The shell is evolute with only a slight overlap of previous whorls. Whorl section is subquadrate, like Pleuronautilus, only depressed. Flanks have conspicuous ribs that may be somewhat...

, from the same time and place as Holconautilus is also similar except for having a wider whorl section and a venter that is slightly concave.

References

• Bernhard Kummel, 1964. Nautiloidea-Nautilida. Treatise on Invertebrate Paleontology, Part K. Geological Soc. of America and University of Kansas press. Teichert and Moore (eds)