450
Journal of Paleontology 91(3):444–466
posterodorsal corner at ~60% total shell length, ventral margin convex; strong ridge starting posterior of umbo, running to posteroventral corner, anterodorsal margin of ridge almost angular, followed by broad groove; shell surface anterior of ridge smooth except for growth lines, posterior side shows rib- bing or wrinkles, resulting from irregular, roughly commarginal thickenings. Juvenile specimen with fine taxodont hinge teeth along entire posterodorsal margin and on oval hinge plate below beak; hinge area in adult smooth. Largest specimen 33mmlong, 17mm high, single valve 7mm wide; a juvenile specimen with taxodont hinge teeth measures 8.3mm in length.
Etymology.—To honor Gian Battista Vai in recognition of his leading role in the modern study of ‘Calcari a Lucina.’
Materials.—Eight specimens from Ca’ Carnè; six from Ca’ Piantè; three valves from Montepetra (MZB 60095), and one valve from Case Rovereti (MSF 1356); see Table 3 for measurements.
Remarks.—We have found mostly disarticulated specimens of this species. One specimen has been figured by Sami and Taviani (2015, fig. 7).
Subclass Heterodonta Neumayr, 1884 Family Thyasiridae Dall, 1900
Genus Channelaxinus Valentich-Scott and Coan in Coan and Valentich-Scott, 2012
Type species.—Channelaxinus oliveri Valentich-Scott and Coan in Coan and Valentich-Scott (2012), (by original designation); Recent, Bahía Santiago, Colima, México.
Channelaxinus sp. Figure 5
Description.—Shells subrectangular, thin-shelled, reaching 20mm in length and 16 in height, only slightly inflated, sculp- tured by irregular growth lines and indistinct, blunt ridge run- ning from umbo to postero-ventral corner; beak prosogyrate, projecting slightly above dorsal margin; anterior margin straight to slightly concave, ventral margin gently convex, postero- ventral corner well rounded, posterior margin gently convex below sulcus, postero-dorsal margin slightly convex, with deep sinus at end of posterior sulcus; posterior sulcus deep, bordered by sharp ridge, area between sulcus and postero-dorsal margin
Table 3. Measurements of Samiolus (s.l.) iohannesbaptistae new genus and species; H=height, L=length,W=width of two valves, except when indicated otherwise.
Locality Specimen
Ca' Carnè MGGC 21910, holotype Ca' Carnè MSF 1119
Ca' Carnè MSF 1120, paratype Ca' Carnè MSF 1073, paratype Ca' Carnè MGGC unnumbered Ca' Carnè MGGC unnumbered Ca' Carnè MGGC unnumbered Ca' Piantè MSF 1071 Ca' Piantè MSF 1072
Ca' Piantè MSF 1355, paratype Case Rovereti MSF 1356
L (mm) H (mm) W(mm) 19.0
12.6 14.6 20.2
16.7 33.2 30.0 25.0
1.1 5.7 (single) 7.5 3 (single) 9.0 3.5 (single) 10.0 4.6 (single)
20.2 (incomplete) 10.2 4 (single) 18.0 8.5
8.8 4 (single) 4.7 1.8 (single) 13.5 4.5 (single) 16.3 7.7 (single) 15.0 8 (single) 13.5 6 (single)
Figure 5. Channelaxinus sp. from the middle Miocene (Langhian) of Ca’ Cavalmagra, northern Italy: (1, 2) left valve (MSF 2113), internal mold and counterpart with small amount of shell preserved; (3) left valve (MSF 1287), internal mold with few shell remains; (4) right valve (MSF 2112) of small specimen.
narrow, with narrow submarginal sulcus; anterior adductor muscle scar thin, elongate, weakly impressed, separated from pallial line, length just over half of shell length; interior radiating striae distinct.
Materials.—Three specimens from Ca’ Cavalmagra (MSF 1287, 2112, 2113).
Occurrence.—Only known so far from the late Langhian of Ca’ Cavalmagra.
Remarks.—A superficially similar thyasirid from the Miocene of the Turin Hills is Thyasira michelottii (Hörnes, 1875), but it clearly differs from Channelaxinus sp. reported here by having a much shorter anterior adductor muscle scar (Zuschin et al., 2001). The extant type species Channelaxinus oliveri differs from Channelaxinus sp. mainly by having a narrower angle between the anterior and dorsal margins and a blunter (less pointed) umbo (Coan and Valentich-Scott, 2012; Oliver and Frey, 2014). This is the first fossil record of Channelaxinus.
Family Lucinidae Fleming, 1828 Genus Meganodontia Bouchet and von Cosel, 2004
Type species.—Meganodontia acetabulum Bouchet and von Cosel, 2004 (by original designation); Recent, in 256–472m depth off northern Taiwan.
Meganodontia hoernea (Des Moulins, 1868) Figures 6, 7
1868 Lucina hoernea Des Moulins, p. 368.
1901 Lucina globulosa var. hörnea Sacco, p. 67, pl. 15, figs. 31–33, pl. 16, fig. 1.
1901 Lucina globulosa var. alta Sacco, p. 68, pl. 15, fig. 4.
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