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Spirocyrtis subscalaris Nigrini, 1977

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Description: Shell conical, smooth with four to six post-cephalic segments. Cephalis hemispherical with a few subcircular pores, a strong 3-bladed apical horn approximately as long as cephalis, and a well-developed, duck-billed vertical tube. Collar stricture indistinct. Thorax inflated with three or four transverse rows of relatively large subcircular pores. Lumbar and post-lumbar strictures clearly visible and often marked by a poreless band. Abdomen and post-abdominal segments inflated, increasing in size distally. Each segment bears four or more transverse rows of subcircular pores of variable size. Termination usually ragged, but rarely a short poreless peristome with very small, irregularly spaced peglike teeth has been observed.
Dimensions (based on 15 specimens): Total length (excluding apical horn) 123-165µ; maximum breadth 65-83µ.
Range: Very rare to few from the Calocycletta costata Zone to Recent.
Phylogeny: Closely related to S. scalaris and S. gyroscalaris and S. subtilis. Probably a branch of this lineage.
Remarks: This species may be distinguished from S. gyroscalaris by its narrower shell and generally fewer segments. The post-thoracic segments of S. subscalaris are more rounded and there is a more or less regular increase in their length distally. Kling (1973) illustrated three North Pacific specimens which he called Spirocyrtis sp. aff. S. scalaris, but these are not quite the same as the tropical form described herein. Sanfilippo and Riedel (1974) described a closely related form, Artostrobium rhinoceros, from the Indian Ocean. In the present material a single specimen (cf. plate 3. figure 4) having a somewhat thorny cephalis has been observed, but none as robust as those illustrated by Sanfilippo and Riedel was found.
Type specimens: Holotype, 77B-8-5, A-W48/1 ; paratype. 77B-21-5. A-T28/4.
Nigrini 1977











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