ANATOMY AND SYSTEMATICS OF CARDIOWCINA 



95 



visceral lobes or pouches are not present in most Lucinidae (Allen, 

 1958), but are found in Parvilucina (Reid & Brand, 1986), and 

 species of Thyasiridae have several pouches (Allen, 1958). Most 

 Lucinidae seem to possess both inhalant and exhalant posterior 

 apertures, produced by mantle fusion (Allen, 1958). In Cardiolucina 

 there is no inhalant aperture, a state found also in Parvilucina (Reid 

 & Brand, 1986). 



Cardiolucina species share three anatomical characters with 

 Parvilucina tenuisculpta, namely; the attachment of the posterior 

 ctenidia to the mantle, the hemispherical visceral pouches and the 

 lack of inhalant apertures. These characters may indicate a possible 

 relationship, but the distribution of most anatomical characters 

 amongst the Lucinidae is not well known. 



Geological range. Eocene (Lutetian) to Recent. 



Comparison with other genera. There has been a tendency to 

 place small, inflated lucinids with both radial and concentric orna- 

 ment, rather arbitrarily into a number of genera such as Phacoides, 

 Parvilucina, Linga and Bellucina. These decisions have usually 

 been made without reference to the characters of the type species. 

 For instance, the status of Bellucina in major taxonomic revisions 

 has varied as follows: 



Phacoides (Parvilucina) section Bellucina - Dall, 1901: 806 



Phacoides (Bellucina) - Lamy, 1920: 21 1 



Linga (Bellucina) - Chavan, 1937: 205; 1969: 496 



Parvilucina (Bellucina) - Britton, 1972: 15 



Lucina (Bellucina) - Bretsky, 1976: 272-3 



Cardiolucina (as Bellucina) has often been considered as a sub- 

 genus of Parvilucina Dall, 1901, type species Lucina tenuisculpta 

 Carpenter, 1864, which ranges from Alaska to Baja California. 

 Hickman ( 1 994) redescribed and illustrated P. tenuisculpta and two 

 other west American species. Although they are small, rounded and 

 fairly inflated, Parvilucina species are thinner shelled and less tumid 

 (T/L 0.29) than all Cardiolucina (T/L 0.38-48) species. Most 

 Cardiolucina have a pronounced posterior sulcus, and sometimes a 

 narrow anterior sulcus, compared to the weak, shallow, posterior 

 sulcus of Parvilucina. Parvilucina has both radial and concentric 

 ribs; the radial ribbing consisting of closely-spaced, low riblets, 

 which are generally weak, but most prominent at the anterior and 

 posterior of the shell. The internal ventral margin of Parvilucina is 

 finely denticulate, compared with the coarser crenulations of 

 Cardiolucina. The lunule in Parvilucina is narrowly lanceolate and 

 asymmetric with the right valve overlapping the left, compared with 

 the shorter, heart-shaped lunule of Cardiolucina agassizi. The hinge 

 plate of Parvilucina is also thinner and the lateral teeth distant from 

 the cardinals. Although a major reappraisal of the relationships of 

 these genera is necessary, evidence suggests that the Parvilucina 

 taxa centred around the type species, represent a clade distinct from 

 Cardiolucina. 



Another genus which should be considered in relation to 

 Cardiolucina is Radiolucina Britton, 1972, (type species Phacoides 

 amiantus Dall, 1901) from the Caribbean. Dall placed this species 

 and the similar West American species L. cancellaris Philippi, 1846 

 in Bellucina. Later, Keen (1971, p. 121) recognised that they were 

 only superficially similar to the type species of Bellucina and 

 placed them in the subgenus Pleurolucina Dall, 1901, remarking 

 that American authors had been slow to recognise Dall's error. 

 Bretsky (1976) confusingly gave an extensive diagnosis of the 

 genus Bellucina based on P. amiantus rather than the type species 

 Bellucina eucosmia. Britton (1972) had previously compared P. 

 amiantus with Bellucina semperiana (Issel) which he considered 

 the type species of Bellucina and recognised that P. amiantus 



represents a distinct and separate lineage within the Lucinidae. For 

 this reason, he erected a new subgenus Radiolucina. The type 

 species, R. amianta has a more elongate shell than most Bellucina 

 species H/L 0.92 (data from Bretsky, 1976, p. 273) compared with 

 about 1.0 for Cardiolucina species, and the shell is less tumid T/L 

 0.33 compared with 0.43 for Cardiolucina. Furthermore, R. amianta 

 has 8-12 broad radial ribs crossed by threadlike concentric lamel- 

 lae, often with intermediate secondary radial ribs in the ventral two 

 thirds of the shell. We agree with Keen (1971) and Britton (1972) 

 that Radiolucina amiantua belongs to a distinct and separate clade 

 which includes several fossil species from the south western USA. 

 Therefore, Bretsky's (1976, p. 272) diagnosis of Bellucina based 

 on P. amiantus should be rejected. 



Some American palaeontologists (Woodring, 1925; Gardner, 

 1926) used the generic name Cardiolucina for some Miocene luci- 

 nids with high beaks and lacking radial ribs. These species are now 

 placed in the genus Cavilinga Chavan, 1937 (see Olsson & 

 Harbison, 1953 p. 85; Bretsky, 1976 p. 265). 



Chavan (1937, 1969) classified Bellucina as a subgenus of Linga 

 de Gregorio 1885, for which the type species is Lucina columbella 

 Lamarck, 1818, a Miocene fossil from France. This is a large, very 

 thick-shelled species with concentric ribs only and a strong posterior 

 sulcus unlike Cardiolucina. 



SPECIES DESCRIPTIONS 



Cardiolucina agassizi (Michelotti, 1 839) 

 Fig. 1 



Cardium agassizi Michelotti, 1839: 17. 

 Lucina agassizi - Michelotti, 1847: 404 pi. 4 figs 4,5, 7. 

 Lucina irregularis Eichwald, 1853: 82-83, pi. 5 fig. 4. 

 Cardiolucina agassizi (Michelotti) -Sacco, 1901: 89-90, pi. 10 figs 



37-39. 

 Phacoides (Cardiolucina) agassizi (Michelotti) - Cossmann & 



Peyrot, 1911: 688-689, pi. 28. figs 83-86. 



Type material. ?Museo di Paleontologia, Rome. 



Type locality. Not given by Michelotti, but Sacco ( 1 90 1 ) records 

 several localities in the Miocene of Italy. 



Description. Shell small, solid, height to 7.4 mm, subcircular, 

 mean H/L 1.03, moderately inflated, mean T/L 0.39, tumidity to a 

 maximum of 2.7 mm on a single valve. Shell inequilateral, ex- 

 tended anteriorly. Deep posterior sulcus with fine concentric 

 lamellae. Shallow anterior sulcus. Lunule heart-shaped, small and 

 shallow. Escutcheon lanceolate with concentric lamellae and a 

 single strong radial ridge. Exterior sculpture of more than 25 faint, 

 radial, rounded ribs with narrow interspaces. There are about 20 

 prominent, concentric lamellae which are often slightly recurved. 

 Lamellae are extremely variable in thickness, degree of projection, 

 recurvature and width of interspaces. Hinge plate thick. Left valve 

 with single posterior lateral tooth, two cardinal teeth and single 

 anterior lateral. Right valve with single posterior and anterior 

 laterals and single cardinal. Ligament extending two thirds of the 

 distance from umbone to posterior lateral tooth. Inner margin with 

 28-30 crenulations and small denticles along anterodorsal and 

 posterodorsal margin. Anterior adductor muscle scar elongate, not 

 buttressed, with pallial line attached near to the ventral tip. Poste- 

 rior muscle scar ovate. Pallial line indistinct. Shell white. 



In the material examined from France we found the concentric 

 ornament to be extremely variable from separated, thin lamellae to 

 clusters of thicker lamellae producing a rugose ornament (see Fig. 



