^^^' 55-] ECTOIIARIA Ai!^D HORMOTOMA. 251 



17. Remarks on the Genera Ectomaeia, Koken, and Hobmotoma^ 

 Salter, luith Descriptioisis of British Species. By Miss Jane 

 Donald. (Commuiiicated by J. Gr. Goodchild, Esq., F.G.S. 

 Eead February 22nd, 1899.) 



[Plates XXI & XXII.] 



Introduction-. 



In my previous papers on the Carboniferous Murcliisonice I have 

 given some account of most of the different genera or sections into 

 which the family Murchisoniidse has been divided. It is not, 

 therefore, necessary to refer to many of these again, as I am here 

 only describing the British members of one of these established 

 genera, namely Bormotoma, Salter,^ and also of the new genus 

 Uctomaria, Koken.^ 



These two genera contain some of the oldest known species of 

 elongated gasteropoda. They are both distinguished from the typical 

 Murchisonice by merely possessing a sinus in the outer lip, instead 

 of having a deep narrow slit with parallel edges; also the lines of 

 growth retreat towards, and advance from, the sinus more obliquely. 

 The protoconch, which throws so important a light upon the 

 affinities of the gasteropoda, is so far unknown in Ectomaria and 

 Hormotoma, neither has it been found out whether these shells have 

 opercula. 



In the present state of our knowledge it is doubtful in what 

 degree these genera are related either one to another, or to the typical 

 Murchisonice. Hormotoma agrees with Murchisonia therein that 

 the sinus gives rise to a band, though it is generally somewhat 

 indistinctly limited ; whereas Ectomai^ia can hardly be said to possess 

 a band, the greatest sinuosity of the lines of growth being merely 

 situated between two keels. Koken does not place Ectomaria in 

 the Murchisoniidse, and it is not clear to which family he would 

 refer it ; apparently it stands in the Eaphistomidae,^ though he 

 states that it, Murchisonia, and Loxonema are closely allied, and he 

 also says that Ectomaria reminds one of certain Glauconioi and 

 Turritellidge. Ulrich «fe Scofield consider that Solenosjpira (which 

 is most probably identical with Ectomaria) may be an early repre- 

 sentative of the Turritellidge, and it certainly bears a strong 

 resemblance to some members of that family. They include it, 

 however, in the Pleurotomariidae, in which family they also place 

 many other elongated forms that have a sinus or slit in the outer lip. 

 I prefer to follow Koken in separating the elongated shells from 

 the shorter Pleurotomarice, and letting them constitute the family 



1 Geol. Surv. Can. ' Canad. Organ. Eem.' dec. i (1859) p. 18. 



2 ' Die Leitfossiiien,' 1896, p. 395. 



3 ' Die Gastrop. des Bait. Untersilurs/ Bull. Acad. Imp. Sci. St. Petersb. 

 ser. 5, vol. vii (1897) no. 2, p. 201. 



