298 MAZATLAN UNIVALVES 



third, in fresh condition, is immature, with the apex but slight- 

 ly recurved, and the radiating striae very coarse, while the 

 concentric laminae are but slightly developed. Epidermis in 

 shaggy layers between the laminae. Long. '34, lot. *3, alt. *18. 

 Hob. W. Indies, passim. Cuba, Sagra. Barbadoes, Dr. 

 Cutting. Senegal, Adanson. Loander, Tarns. St. Vincent, 

 W.Africa, Schmidt. Lobos Is., Peru; on stones, among 

 coarse sand, 17 fm. ; Cuming. Panama ; 14 sp. on stones 

 and shells near low water mark, with thin attached valves ; 

 C. B. Adams. Mazatlan ; extremely rare, off Spondylus j 

 L'pool Col. 

 Tablet 1469 contains the 3 specimens. 



348. HIPPONYX PLANATUS, n. s. 



H. t. valde planatd t subovali, alba ; vertice anfr. ii. rapids 

 augentiLus, lateraliter incumbentibus, interdum persistente ; 

 t. jwniore sparsim radiatim costatd ; postea laminis concentricis 

 a sulcis radiantibus indentatis, ad marginem t. juniore profunde, 

 t. adultd vix serratis ; epidermide tenui, laminas intercalante ; 

 intus valde politd, cicatr. muse, angustd, circulari, regione 

 capitis interrupt^ ; margins producto, simplici, intus rotundato, 

 extus tenuissime serrato ; valvd inferiore tenui (t. juniore) 

 multo minore, usque ad regionem eicatrieis solum continud. 



Three very small specimens of this species were found in 

 the Spondylus washings ; but Mr. Darbishire was fortunate 

 enough to find a beautiful young shell in a Lithodomus bur- 

 row in situ ; too late for the list in the Proc. Zool. Soe. 

 Afterwards some large adult upper valves were brought by 

 Mr. Bridges. All agree in the extreme flatness, torque-shaped 

 muscular scar, finely cancellated laminae and rounded but 

 spreading margin, The spiral apex, being recumbent and 

 rather solid, has remained on two of the specimens, a very 

 unusual thing in the genus. It is known from even the flattest 

 specimens of H. antiquatus by the shape of the scar, spreading 

 margin, recumbent apex, and sparse radiation, of the earlier 

 portion. The youngest shell is '07 across, with the Helicoid 

 whirls about '015 in diameter. The most perfect specimen in 

 Mr. Cuming's collection (not the largest) measures long. '73, 

 lot. '64, alt. '17. 



Hob. Mazatlan ; on Spondylus, extremely rare ; L'pool Col. 

 Bay of Panama, T. Bridges, Mus. Cuming. 

 Tablet 1470 contains the youngest and an adolescent sp. 



