Perkinsoceras
Encyclopedia
Perkinsocerasis an endocerid genus from the Middle Ordovician (Chazyan) of Champlain Valley
established by Flower in 1976, which he added to his Allotrioceratidae based on certain similarities to Williamsoceras
and Cacheoceras which had been added previously.
Perkinsoceras is characterized by a large ventral siphuncle
in broad contact with the ventral margin of the phragmocone -the chambered portion of the shell- which is expanded into a Nanno type apex, and by a broad longitudinal ventral process about which the endocones are draped. Perkinsoceras has what have been interpreted as tubules that form where the endocones impinge on the process, a feature also interpreted in Williamsoceras, Cacheoceras and the distinctly unique Allotrioceras
Perkinsoceras differs from the generally similar Chazyoceras
by its ventral process -absent in the latter, and by its more bulbous nanno type apex. Williamsoceras and Cacheoceras differ in having a straight cameroceras type apex without the expanded siphuncle. Allotrioceras differs by its vertical median partition separating the two lateral endocones. Perkinsoceras has a single set of endocones
Two species of Perkinsoceras have been described, both early Middle Ordovician (Chazyan) in age, both from Vermont. P inflatum comes from the Crown Point Limestone, 1/2 mile south of Ferrisburg Vt. The holotype is in the Paleontology collection of the New Mexico Museum of Natural History and Science. P foerstei comes from Isle La Motte. Its holotype is at the U.S. National Museum in Washington D.C.
Champlain Valley
The Champlain Valley is a region of the United States around Lake Champlain in Vermont and New York extending slightly into Quebec, Canada as part of the St. Lawrence River drainage basin drained northward by the Richelieu River into the St...
established by Flower in 1976, which he added to his Allotrioceratidae based on certain similarities to Williamsoceras
Williamsoceras
Williamsoceras is an endocerid that Rousseau Flower added to his Allotrioceratidae on the basis of having a vertical partition within the siphuncle, known as a ventral process, with inter-connecting tubule-like structures along its margin where intercepted by endocones...
and Cacheoceras which had been added previously.
Perkinsoceras is characterized by a large ventral siphuncle
Siphuncle
The siphuncle is a strand of tissue passing longitudinally through the shell of a cephalopod mollusk. Only cephalopods with chambered shells have siphuncles, such as the extinct ammonites and belemnites, and the living nautiluses, cuttlefish, and Spirula...
in broad contact with the ventral margin of the phragmocone -the chambered portion of the shell- which is expanded into a Nanno type apex, and by a broad longitudinal ventral process about which the endocones are draped. Perkinsoceras has what have been interpreted as tubules that form where the endocones impinge on the process, a feature also interpreted in Williamsoceras, Cacheoceras and the distinctly unique Allotrioceras
Allotrioceras
Allotrioceras is a tubular fossil from the middle Chazyan of New York state, collected by Rousseau H. Flower and included by him in the Endocerida and placed in a new family, the Allotrioceratidae...
Perkinsoceras differs from the generally similar Chazyoceras
Chazyoceras
Chazyoceras is a moderately large endocerid included in the Endoceratidae with a Nanno type apex and a ventral siphuncle with a holochoanitic wall, characteristic of the family. The siphuncle swelling at the apex is subtriangular in longitudinal profile. Endocones are of medium length.Chazyoceras...
by its ventral process -absent in the latter, and by its more bulbous nanno type apex. Williamsoceras and Cacheoceras differ in having a straight cameroceras type apex without the expanded siphuncle. Allotrioceras differs by its vertical median partition separating the two lateral endocones. Perkinsoceras has a single set of endocones
Two species of Perkinsoceras have been described, both early Middle Ordovician (Chazyan) in age, both from Vermont. P inflatum comes from the Crown Point Limestone, 1/2 mile south of Ferrisburg Vt. The holotype is in the Paleontology collection of the New Mexico Museum of Natural History and Science. P foerstei comes from Isle La Motte. Its holotype is at the U.S. National Museum in Washington D.C.
References
- Flower, R.H 1976. Some Whiterock and Chazy Endooceroids, Memoir 28, Part II, New Mexico Bureau of Mines and Mineral Resources, Socorro, New Mexico
- Flower, R. H. 1955. Status of Endoceroid Classification; Jour. Paleon. V 29. No.3, pp 327–370, May 1955