304 CRETACEOUS PELECYPODA 



in 18865 in Asiatic Society's Journal, v, p. 750 ; consequently the latter will have 

 probably to be changed. , Conrad (in Journ. Am. Conch., iv, p. 249,) proposes 

 for Mycetopus emarginatus, Lea, the generic name Solenaia with the following 

 characteristic — " elongated, thin, gaping anteriorly, hinge with a long acicular lateral 

 tooth in each valve, slightly developed." I have not seen the Siam species, but 

 the Cachar Anodonta soleniformis of Benson, which is very closely allied to the 

 former, has no lateral teeth. 



List op cretaceous species oe TlNiONWyE. 



l.— Unio CortmeUana, d'Orb., Prod, ii, p. 106, (U. Martinii, Pal. fran9., cret., vol. iii, p. 127, 

 pi. 384, non idem. Sow. apud Fitton). In his figure of a cast specimen d' Or bigny does not 

 show any distinct trace of the existence of a posterior tooth, but there are two unequal sub-anterior 

 in the left valve, the anterior being very large, the posterior very small ; this kind of hinge, if 

 correct, would indicate the species to belong to Margaritana. D' Or big ny first identified this 

 species with one from the Wealden beds, but then separated it as distinct, which, judging 

 "from figures only, certainly appears to be more correct; it is from the so-called Urgonien or 

 Upper Neocomien. 



%.— Unio creataceus, Zittel, (Denksch. Akad., Wien, xxiv, pt. ii, p. 158). I have not seen 

 the hinge of this species, and I am not certain whether it is quite correctly figured by 

 Zittel. The species exhibits two unequal anterior teeth, or rather a large bifid tooth, its anterior 

 portion being smaller than the posterior, and there is only a single elongated rather thin posterior 

 tooth ; besides that the anterior muscular scar is situated on a raised lamina. In all species of 

 Unio the posterior tooth of the left valve is double and the one of the right usually single. The 

 form of the anterior teeth varies almost ad infinitum. It is probable that this cretaceous species 

 has to be separated into a distinct genus, but better materials are required for that purpose than 

 those now accessible. The species is from the Alpine-Gosau formation, ( TuronienJ. 



3.— Unio acutus, Schafhseutl (Siid-Bayerns Leth. Geog., 1863, p. 163). A small form 

 resembling a Cardinia ; the hinge-teeth are not observable, and the generic determination, there- 

 fore, doubtful. The author quotes it from a locality from which in other places he describes 

 cretaceous shells, but whether the present species is really a cretaceous form no one could 

 guarantee. 



^.— Unio Nordmanni, Eichw., (Leth. ross., x livr., p. 609,) is stated to be from a white chalk 

 of the Crimea. The figure representing the species is peculiarly ovate and tumid, but hardly any 

 one could suspect a Unio in it. 



5-14.— Lea (Proc. Acad. Nat. Sc, Phil., 1868, No. 3, p. 162,) describes from some fresh-water 

 cretaceous beds of New Jersey the following ten species, based upon a material consisting of 

 about forty cast specimens collected by Prof. Co^q '.— U7iio 7iasutoides, radiatoides, suh-rotundoides, 

 carriosoides, humerasoides, RoanoJcoides , ligamentinoides, alatoides, Anadonta grandioides, and 

 corpulentoides. The author cautiously remarks that the descriptions must necessarily be imperfect, 

 being taken only from casts. He also states that they strongly recall the forms found by Mantell 

 and others in Wealden deposits of England. Certainly, whoever will succeed hereafter in recog- 

 nising Mr. Lea^s species may call himself an unusually successful discriminator of fossils. 



15.— ^. pennltimus, Gabb, Pal. Calif, i, p. 182, from the Tejon group of California. 



16.— C/-. Eulhardii, Gabb, Pal. Calif, ii, p. 190, from the so-called Chico group of Vancouver 

 Island. 



