Benson 1966 - Dictyoceras bombus

Cephalis spherica1, with small, circular, hexagonally arranged pores and rough surface; in a few specimens nearly hyaline; separated from a broad pyramidal thorax by a distinct collar stricture. A long, straight to slightly curved, vertical, conica1, to three-bladed apical horn originates from the top of the cephalis in a dorsal position and extends from the apical bar which is a dorsally located internal columella.A small, conical to three-bladed vertical spine originates from the base of the cephalis at the collar stricture. Four small, circular collar pores at the base of the cephalis, separated by heavy bars; collar ring heavy. Thorax pyramidal with flat to slightly concave inward sides extending between the dorsal and primary lateral thoracic ribs which are surmounted by low, latticed keels. The three basal spines are three-bladed to conical and are joined by lattice to the thorax; they extend horizontally or slightly upward from the distal terminations of the ribs and originate from about the middle of the thorax or slightly above. The latticed keels projecting upward from the thoracic ribs bifurcate and diverge downward at the point where the basal spines originate; adjacent branches of rib keels curve downward toward one anther and meet, forming a latticed keel projecting horizontally from the septal ring separating thorax and abdomen. Between branches of each keel is a flat, subtriangular, latticed portion of the thorax, the base of which is represented by the inner septal ring separating thorax from abdomen; this portion of the septal ring is without a keel projecting horizontally from it. The thorax, therefore, has six sides divided by keels, three larger ones with a curved distal margin, each between adjacent thoracic ribs, and three smaller, subtriangular sides, each located between the lateral distal margins of adjacent larger sides. Pores of the thorax small, equal, hexagonal to subcircular, hexagonally arranged. Surface of thorax smooth except for the low, latticed keels. Abdomen broad, subcylindrical, smooth, separated from thorax by a distinct constriction and an inner septal ring which is not coplanar. Pores of the abdomen less regular and slightly larger than those of the thorax, arranged more or less in transverse rows.

Measurements: based on 5 specimens from stations 64 and 81: length of cephalis 23-31 µm, of thorax 66-112 µm, of abdomen 47-74 µm; breadth of cephalis 26-31 µm, of thorax 79-144 µm, of abdomen 97-141 µm; length of apical horn 12-34 µm, of vertical spine 10-16 µm, of basal spines 25-37 µm.

Remarks: Theopilium pyramidale Popofsky differs from the Gulf species only in the absence of the three, wing-like basal spines, each of which in the Gulf specimens originates from the apex of the triangular outline formed by the latticed keels on the thorax. Positive identification of the Gulf species, which definitely belongs in the genus Dictyoceras Haecke1, with Popofsky's species must await examination of Popofsky's type material in order to determine whether or not the lack of basal spines is constant within his species.

Distribution: This species is very rare in the Gulf but is present as far north as station 192; therefore, it is cosmopolitan in the Gulf with apparently equal affinity for oceanic waters of the southern Gulf and waters of slightly higher salinity and temperature of the northern Gulf. It is absent at stations 27, 90, 95, 99, 130, 191, 194, and all those to the north. Its absence at most of the marginal localities indicates its preference for offshore, more nearly oceanic waters. It does not appear to be associated with upwelling areas in the Gulf. Popofsky (1913, p. 376) reported Theopilium pyramidale from the tropical portions of the Atlantic and western Indian Oceans. If the Gulf species is the same as Popofsky's species it is apparently widespread in Recent tropical seas. \ From: Benson, 1966, p. 419-422; pl. 28, fig. 11:Dictyoceras cf. pyramidale (Popofsky)?Theopilium pyramidale Popofsky, 1913, Deutsche Sdpolar-Exped., vol.14, p. 376, Pl. 37, fig. 1.

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