Calvert Formation, Zone 10


The Zone 10 Material

The specimens below are illustrative of Zone 10 material. Hot spots in the photos go to additional photos, drawings and names of each species.

Where there are rulers without numbers, the units are millimeters.

As is obvious from the specimens, some layers of the Calvert Formation are shells with a little sand filling the cavities. The material is loosely consolidated and the specimens illustrated have all been stabilized with glue.

The number of species can be significant. In the first piece there are thirteen bivalves, twelve gastropods, and one species each from hydrozoa, bryozoa, condrichthyes (sharks in the form of a tooth), and maxillapoda (barnacles). Heres is the list of species in this first specimen.

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Anadara subrostrata

Astarte cuniformis




There are several Astarte species in Zone10 including A. parma, A.vicina, and A. cuniformis.




Astarte vicina

Astarte parma


Cardita granutata



Chlamys madisonius

Corbula idonea






Corbula inaequalis

Glycymeris parlis



This species is only present in the lower portion of the Calvert formation.


Melosia staminea




Isognomon maxillata

Maracrassatella melinus


Mercenaria rileyi

Stewartia anodonta





Cardium laqueatum

Dosinia sp.


Carditamera arata

Venus mercenaria


Clorbula elevata

Lirophora latilirata (Venus clam)

Tellina producta




Chrysodomus patuentensis

Crucibulum pileolum and costatum


These specimens are 1 cm in length.





Cylichna calvertensis

Polinices heros


These tiny snails are very common. I sift the sand remaining after excavating larger specimens to find them.




Drilla pseudebunea

Nisa lineate



Siphonalia devexa

Turritella indentata






Turretilla plebia

Turretilla variabilis

Vermetus virginicus



These turritella species are very common in Zone 10. Having said that, T. indenta is less common than T. plebia or T. variabilis

T. variabilis has been divided into several varities but I've made no attempt to distinquish them here.




Voluta cassidula

Typhis acuticosta


Ecphora tricostata

Xenophora conchliophora




This genus is extant along the southern Atlantic coast in the U.S. What is unique about this specimen is the small stones the animal used to camouflage itself are still present. Usually the camouflage is lost on fossils. In this instance the size of the pebbles increase as the animal grew.


Siphonalia sp.

Busycon spiniger





Fissuridea marylandica

Pleurotoma bellacrenata

Epitonium pachpleuro



Calliostoma virginicum

Terebra curvilineata v. calvertensis


Scaphella solidaria





Dentalium attenuatum

Dentalium caduloide

Cadulus thallus







Hydractinia multispinosa


A paper ( says that the presence of this hydrazoa is indicative of the presence of hermit crabs. This species is very common in Zone 10.









  This is not a piece I found but is from the North Museum of Science and Natural History in Lancaster, PA. I came across this bryozoan encruting a scallop shell in the Plum Point collection while entering specimens in a digital database. It seems to be a new species of bryozoan. The genus is Schizoporella. These other specimens are a result of looking for another example of the bryozoan to confirms the location and strata. If you have a similar specimen from Zone 10 of the Calvert Formation, please contact me.    



List of species in the first specimen:

Bivalvia (Pelecypoda)

Melosia staminea
Astarte parma
Astarte cuneiformis
Anadara subrostrta
Eucrassatelal turgida
Mercenaria mercenaria
Chlamys madisonius
Corbula inequalis
Corbula idonea
Cardium laqueatum
Parvilucina sp.
Tellina sp.
Cardita granutat


Xenophora conchyliophora
Turritella plebia
Turritella variabilis
Turritella indenta
Scaphella solitaria
Polinices heros
Echphora tricostata
Crepidula fornicata
Crucibllum costatum
Three small unidentified snails


Hydractinia multispinosa, a hydrozoa,

Unidentified bryozoa

Unidentified shark's tooth

Unidentied barnacle plates


Marvacrassatella melinus Stewartia anadonta