272 CRETACEOUS PELECTPODA 



XXVIII. Family— ASTABTIB^. 



Animal elongately ovate or sub-trigonal, with the mantle margins thickened, 

 disunited below in their entire extent, posteriorly with a single opening ; foot laterally 

 more or less compressed and sharpened below, pointed at the end, and in young 

 specimens sometimes with a byssal groove at the posterior base ; palpi two pairs, 

 generally narrow, sub-triangular, striated ; gills one pair on each side, the leaflets 

 being unequal, the interior mostly larger, or sub-equal, anteriorly rounded, poste- 

 riorly pointed and more or less produced. 



The shells are thick, solid, equivalve, with the cardinal teeth always well 

 developed, 2-3 in each valve ; lateral teeth are sometimes present on one or on both 

 sides, ligament always external, strong ; muscular scars ovate, the anterior usually 

 with a small deep superimposed pit, produced by the retractile muscle of the foot ; 

 pallial line entire. All the species are marine. 



The genera which have to be referred to the present family are very numerous, 

 and the greater number of them is only found in a fossil state. Merely in order 

 to facilitate the grouping of the different types, I shall here provisionally introduce 

 two sub-families under the names astaetinje and caeditinjE. Of the former the 

 genus Astarte may be taken as the type ; the shells included in the sub-family 

 are distinguished by a sub-trigonal or roundly oval shape, and a smooth, concentri- 

 cally striated or sulcated surface. The cahditinm^ with the typical genus Cardita^ 

 include shells of a roundly ovate or elongated form, always provided with radiating 

 ribs or stride. In the former sub-family I shall enumerate the following — Mega- 

 lomus, Fachydomiis, Megalodon, r'sub-g. Eu,- Neo,- and Fachy-megalodon), Astar- 

 tila, Conchodon, Tachyrisma, Opis, Opisoma, Far-astarte, Cypricardinia, Anoplo- 

 phora^ Cardinia, Trigonodus, Fuloxa, Astarte, (sub-g. Gonilia)^ Grotriania, Free- 

 conia, Gouldia, Alvemus, Goodallia, Lutetia, Mycromeris, Goodalliopsis, and 

 Woodia ; to the latter will be referable Matheria, Fleurophorus, Falceocardita, 

 jpieuromeris, Miodon, Fteronieins, Cyclocardia, Venericardia, Cardita, Mytilicardia, 

 Carditamera, I have already observed that the arrangement of the two sub- 

 families is to be considered only a provisional one. 



The whole family, as it now stands, belongs decidedly more to the past epoch 

 than to the present one. Our knowledge of the organisation of the animals of the 

 few genera examined is as yet rather unsatisfactory, and moreover the different 

 accounts are somewhat contradictory. 



Taking notice of the anatomy of the animals of the Pelecypoda in a classi- 

 ficatory point of view, the number, position, and form of the siphons, or of the 

 branchial and anal openings, has been considered as one of the most important 

 characters. Of the astastinje we know some of the animals of Astarte and 

 of Gouldia, the only two recent genera - besides Woodia- of which I have met with 

 the description of the animals. Eorbes and Hanley, in their admirable History 

 of British MoUusca, state that Astarte has two siphonal openings, and this state- 

 ment appears to have been generally accepted. H. and A. Adams in their 



