Yol. 65.] THE GENUS LOXONEMA. 213 



a sinual band. The likeness to Ectomaria is much less, for though 

 the lines of growth continue without break, the whorls are lower 

 and are ornamented by keels. Loxonema is further distinguished 

 from both these genera in having a comparatively shallow, instead 

 of a deep tongue-shaped sinus. Dr. Perner describes a new 

 genus under the name of Sinuspira, which he considers intermediate 

 between Ectomaria and Loxonema ; it resembles the latter in form 

 and in having smooth whorls, -but it has a much deeper sinus. In 

 this character it is like both Ectomaria and Hormotoma, and more 

 especially the latter, as the lines are similarly curved instead of 

 being straight as in the former. It is distinguished from Hormotoma 

 by not possessing so distinctly defined a band, and from Ectomaria 

 by having high and smooth whorls. 



In this country Ectomaria appears to make the earliest appearance, 

 occurring in the Durness Limestone, 1 where it is represented by 

 E. pagoda, Salt. var. peacliii, Don. and var. orientalis, Don., and 

 by E. antiqua, Don. 2 Hormotoma was recorded from the same 

 horizon, 3 but I am informed that a mistake was made with the label 

 of H. salteri, Ulrich & Scofield, when the specimens were sent to- 

 me from the Edinburgh Museum, as they were really from Canada. 

 The other two species from Durness are only referred to the genus 

 with a query. I have not met with undoubted species of Hormotoma 

 earlier than the Llandeilo formation. Loxonema, so far as I know 

 at present, appears first in rocks of Bala age. 



In America both Hormotoma and Ectomaria ai*e recorded 

 from the Calciferous Formation (Tremadoc). They do not seem 

 to be known earlier than the Bala in the Baltic Provinces of 

 Bussia. The earliest species referred to Loxonema in America are 

 L. murrayanurn, Salt, and L. jersey ense, Weller, both from the 

 Trenton : neither of them is represented as having the lines of 

 growth characteristic of Loxonema. In Sweden, Loxonema dalecar- 

 licum, Lindstr. is recorded from the Lejrtcena-Kalk (Upper Bala ?) ; it 

 greatly resembles the British species L. striatissimum, Salt., from 

 the Upper Bala, and L. grayianum, from the Lower Llandovery. 



Thus, it may be observed that, judging from our present evidence, 

 Loxonema appeared later than either Ectomaria or Hormotoma. 

 Also there is no evidence of Loxonema being derived from either of 

 these genera, though they may all have originated from a common 

 stock; as yet, however, we have not sufficient material to afford grounds 

 for the establishment of such a theory. It is possible that Ectomaria 

 and Hormotoma may each have had a distinct line of ancestry, if 

 the former be a primitive relation of the Turritellidse, as has been 

 surmised by Ulrich & Scofield. The recent Turritellidae, however, 

 show no trace of primitive origin and are Taenioglossa ; while the 

 Murchisoniidse are supposed to have been Bhipidoglossa, on account 

 of their resemblance to the recent Pleurotomariidse, which have 

 distinctly primitive characters. 



1 Quart. Journ. Geol. Soc. vol. lv (1899) pp. 254 & 270. 



2 Ibid. vol. lviii (1902) p. 319. 



3 Ibid. vol. lv (1899) p. 262. 



