FIFTH, OR AOAS S'l II. 



first mode of development t">>r two and a quarter volutions. The incre 

 gradual, bo that well defined pilsB are not produced until the last ui' the third or 

 tarter of the fourth whorl. An English specimen of variety A bas large 

 tubercles <>n the second quarter of the third whorl. These continue ;it long 

 intervals, only about two t" a quarter of :i whorl. The true piloa do not begin 

 mtil the third quarter of the fourth volution Even then these are 

 lingly oblique and fold-like, and, though thej booh assume the asp< 

 true pilse, retain their obliquity until the second quarter <>t' the fifth volution. 

 Another English specimen shows acceleration by developing similar tubercles 

 on the last quarter of 1 1 1 • - second volution, and also by the development <>f per- 

 itraighl pilaa <>n the second quarter of the fourth volution. A third speci- 

 men of variety E, from Lyme Regis, has tubercles beginning on tli" last quarter 

 of tin- second whorl, and perfect pilaa mi the last part <»t the first quarter "t the 

 fourth \ • >l 11 1 i< <n 



\ m. Sniithi 



Tin- British Museum i card with several young specimens of the 



which ;it first nppear to be identical with the lull grown 



They have short living chambers, becoming i •«• 01 less contracted 



.it th<- apertures, and fold-like pilaa with striationa They have not, however, the 

 • mi of the \ < 1 1 1 1 1 _r ol Plate \ III Fig 10, L3, nor similar 



ratural digi tat ions, and the living chamber i> about three fourths of :i volution in 

 It i* interesting t«> note here the fact, that acceleration in the develop- 

 ment of the tubercles and pilaa occurs in variety E, which has more involute 

 shells than other vari< 



• •• sutures, and the number <>t specimens usually 

 exhibiting thesi re also favorable for testing tin- diagnostic value "i the 



of ili" lobes and saddles in the definition of the species. V7e have 

 ■ numbers of measurements, <>i which 1 1 1 « - following ar< 

 The ii • the differences between the abdominal and superior lateral 



ni'l superior lateral saddles. The Abdominal lobe and infe- 

 dways longer, the fraction expresses at the same time 

 te lengths in equal division* "t these two 

 pecimen ■ B, from Robin Hood's Bay, bas three sutures on the 



third and t««» on the fourth quarter of the fifth volution, with :i differei 

 only two fifths between lobes and saddles, and one septum on 1 1 1 • - third 

 t ♦ • r . in which the lob Idles remaining unchanged 



pflingen has lo om one fifth to one third, and 



saddles from one -ixtli t . . two thirds A specimen <>i I I, has 



of it- sutures, l>ut either two fifths <>\ one hall b< 

 the lobes, and one fifth >>\ one third between the saddles, Compm 



f tlii- 



•:i Boll, llfl 



the lobes hi<1 - iddles, « ill 



