Miltha romaniae Adams & Adams 1857, sp. nov.

Miltha (s. lat.) romaniae sp. nov.

urn:lsid:zoobank.org:act: 2B925733-211D-4EBA-9212-DAB02264F43C

Fig. 11

Diagnosis

Shell oval, flat, reaching 30 mm in length, with anterior and posterior groove producing narrow anteroand posterodorsal areas; umbones little elevated, pointed, slightly prosogyrate, displaced anterior at about ⅓ of shell length; anterodorsal margin nearly straight; anterior margin gently rounded, with smooth transition to convex ventral margin; posterodorsal margin almost straight, with angular transition to posterior margin; posterior margin with indent at end of posterior groove; ventral commissure slightly undulating; external surface covered by numerous densely-spaced, fine commarginal ribs that become stronger toward the outer margin; at antero- and posteroventral margin, the ribs their interspaces are often covered by obliquely tangential thread-like ridges; no radial sculpture; aams thin, elongate, reaching just below mid-line of shell, deviating from pallial line at an angle of about 15°; pallial line entire, running close and parallel to ventral margin.

Etymology

Named after ‘Románia’, Latin name for ‘Romagna’ (Emilia-Romagna region) where a number of key Calcari a Lucina sites are located.

Material examined

Holotype

ITALY – Emilia-Romagna • Ca’ Cassano; MSF 2346, a left valve with preserved shell material.

Paratypes

ITALY – Emilia-Romagna • 9 specs; Ca’ Cassano; MSF 2345, MSF 2347, MSF 2348, MSF 2362 (L = 30, W = 7.0 mm), MSF 2363 (L = 29.2).

Remarks

Miltha (s. lat.) romaniae sp. nov. shows many characteristics of the genus Miltha, except that it has a very thin and only moderately long aams, whereas typical species of Miltha have a very long and lenticular aams that widens in the center, and reaches almost to the ventral margin (Ludbrook 1969; Vokes 1969). In addition, most species of Miltha have a narrower posterodorsal area, and they are significantly larger (70 mm and more) compared to Miltha (s. lat.) romaniae (40 mm max). Miltha (s. lat.) romaniae has a slightly undulating ventral margin (Fig. 11F) but seems not to show differences in inflation between left and right valves, as in Miltha (Vokes 1969). Also the subgenus Miltha (Matanziella) Frassinetti, 1978, is larger and has a broader aams than Miltha (s. lat.) romaniae, and furthermore differs by lacking the distinct grooves separating the antero-and posterodorsal areas (Frassinetti 1978). Species of Miltha show differences in inflation between left and right valves. This was not observed in the few available, articulated specimens of Miltha (s. lat.) romaniae. However, Vokes (1969) noted that this feature appears only later during ontogeny, and is only detectable in specimens larger than about 25 mm length. With the largest available articulated specimen of Miltha (s. lat.) romaniae being about 32 mm long, the lack of this feature might just be a matter of its small size relative to Miltha. Due to the differences outlined above, Miltha (s. lat.) romaniae might represent a new genus or subgenus closely related to Miltha, but with its hinge area remaining unknown, we prefer to assign this species to Miltha (s. lat.).

Stratigraphic and geographic range

Upper Miocene, northern Italy.