MAZATLAN UNIVALVES 275 



This beautiful and rare species combines the form and habit 

 of growth of the Atlantic C. porcellana, Linn, with the very 

 remote apex of C. adunca. This character also separates it from 

 C. arenata, Brod. (found at S. W. Mexico, P. P. C., but not at 

 Mazatlan,) to some forms of which it bears a close resemblance. 

 C. arenata occasionally develops an apical hole within, (Mus. 

 Cum.) : but is never seen with the very oblique growth of this 

 species. The nucleus is like a regular, somewhat tumid Plan- 

 orbis ; shewing the whirls within, and measuring about '02 in. 

 across. The enlargement is regular, and the young shell has 

 exactly the characters of the adult, except that the apex, though, 

 separate, is nearer the margin. Only two very young specimens 

 and one adolescent were found in the Mazatlan collection ; a 

 larger one, probably from the same collection, was obtained 

 from a shop : and some very fine ones are in the Cumingian 

 Museum. The smallest specimen is ' 12 in length ; the largest 

 long. '95, lat. '64, alt. '35. 



Sab. Real Llejos, Cuming, teste Broderip : (but Gulf of Cali- 

 fornia, teste Mus. Cum.) Panama, 1 sp. C. B. Adams. 

 Mazatlan ; extremely rare, jun. on Spondylus ; Upool Col. 

 Tablet 1355 contains a young sp. 1356, an adolescent sp. 



338. CEEPIDULA ADUNCA, Sow. 



Tank. Cat. no. 828, App. p. vii. (Crypta a.) H. & A. Ad. Gen. 



i. 369. 

 = Crepidula solida, Hinds, Voy. Sulph. Moll, p, 53, no. 218, 



pi. 16, f. 7, 8. (Crypta s.) H. $ A. Ad. Gen. i. 369. 

 = Crepidula rostriformis, Gould, JExp. Shells, 1846, p. 14. 

 Jun. = Crepidula rostrata, C. S. Ad. Pan. Shells, pp. 235, 



320, no. 353. (Crypta r.) H. Sf A. Ad. Gen. i. 369. 

 Jun. var. = Crepidula uncata, Mke. in Zeit.f. Mai. 1847, p. 184, 



no. 34. 



= Crepidula incurva, var. P. P. C. Cat. Prov. 

 Garnotia solida, Gray, Gen. 'Moll. IB. M. p. 117. 



The very remarkable form of this species has attracted the 

 attention of six celebrated naturalists, each of whom have im- 

 posed upon it a separate name. The first three specific names 

 are identified from the types ; the other two from the very accu- 

 rate descriptions given. The irregular corrugations of C. B. Ad. 

 are abnormal, as are also the three ridges of MenJce. Normally, 

 the shell is quite smooth, with a rather glossy epidermis ; with 



