& HAZATtAN UNIVALVES 



Hob. Panama, rare, C. IB. Adams. Mazatlan ; extremely 

 rare ; L'pool Col. 



Tablet 1078 contains the two smallest specimens. 1079, the 

 largest specimen. 



GENUS SIMULA, Defr. 



Vide A. Ad. Monogr. Rim. in Proc. Zool. Soc. 1851, p. 226 : 

 H. fy A. Ad. Gen. vol. i. p. 451. JN"on Simula, Lowe, Proc. 

 Zool. Soc. 1854, p. 181. 



This beantiful genus is exactly intermediate between Fissu- 

 rella and Emarginula ; representing permanently the young 

 state of Fissurella, and, apparently, in its own young state 

 resembling Emarginula. Like other Oolitic forms, it has 

 hitherto been found recent only in the Eastern Seas. 



281. SIMULA MAZATLANICA, n. s. 



~R. t.parvd, oblongd, compressd, conic d ; albidd, epidermide 

 tenui albo-fuscd indutd ; apice planatd, angustd ; superficie 

 tenue cancellatd, cancellis quadratis ; fissurd subelongatd, sub- 

 quadratd, intus subovali, callosd, exlus interdum vix lobatd, ex 

 guadrante dimidium versus totce ab apice ad marginem longitu- 

 dinis continud ; foramine lineis incrementi decussato apicem 

 versus currente ; margine tenue crenulato. 



This shell would have been taken for the young of Glyphis 

 insequalis, which in general appearance it greatly resembles ; 

 but that fortunately the young of both that species and G-. alta 

 were found, differing in the following^particulars. In the 

 Glyphides, the hole is close to the apex, comparatively large 

 and solid, and so arranged that as the hole increases, the apex 

 is eaten away. In the Bimulse (of which 12 specimens were 

 found of different ages) the slit occupies a portion extending 

 from one-fourth to one-half of the entire length from apex to 

 margin ; and though the largest shell is much larger than the 

 Glyphis, the apex still continues in tjie same relative position, 

 and there is a channel running up to the vertical portion, 

 shewing the lines of previous slits as in Pleurotomaria. The 

 lines of growth on the young shell seem to shew that at one 

 time it took the form of Emarginula, afterwards enclosing its 

 slit. In this respect it is the reverse of Scissurella, which 

 (as appears from specimens found in the Teneriffe dredgings) 

 when young is like Simula or Trochotoma, when adult like 



