48 PROCEEDINGS OF TIIE MALACOLOGICAX SOCIETY. 



growth gives rise to the formation of a distinct band on all the 

 whorls similar to that on Pleurotomaria. The aperture, instead of 

 being rounded, as in the latter genus, is oblong, its length equalling 

 abonl twice the width, and it is slightly channelled below. The type, 

 MurcMsonia eoronata, Groldf., is regarded by Mr. Whidborne as one of 

 the numerous varieties of If. turbinata, Schlot., which are all more 

 robust shells, with more rapidly increasing whorls, than any of the 

 recent forms. These last are also further distinguished by having 

 merely a deep sinus, instead of a slit in the outer lip, and this sinus 

 never gives rise to the formation of a distinct band, the lines of 

 growth continuing from suture to suture without break ; the aperture 

 is shorter, being more or less quadrangular, and very slightly 

 channelled below. 



There are many genera with a sinus in the outer lip, to which 

 it is not here necessary to refer, because they differ greatly in other 

 characteristics from the shells under consideration. 



Several groups, however, have been placed in the family Murchi- 

 soniida% that have a sinus and not a slit in the outer lip, and 

 consequently no distinct band on all the whorls, viz. : Ectomaria, 

 Koken, Pseudomurchisoma, Koken, Hypertonia, Donald, etc. In 

 Ectomaria the shell is slender, ornamented by spiral keels, the 

 sinus is situated rather low in the outer lip, and it does not form 

 a band on any of the whorls. JPseudomurchisonia has merely a sinus 

 in the earlier whorls, but in the later ones this gives rise to a band. 

 Hypergonia is characterized by a more or less slender form ornamented 

 with keels, a sinus in the upper part of the outer lip situated between 

 two of the keels, and by the absence of a distinct band. The outer 

 lip of the recent shells advances, and the sinus is deeper at the 

 margin than the form of the lines of growth on the whorls would 

 lead one to suppose. It is therefore very difficult to make a just 

 comparison wiih fossil groups, in which the aperture is rarely entire. 

 A notable exception occurs in the case of MurcMsonia snbsulcata, 

 De Kon., in which the outer lip is remarkably well preserved, and 

 the sinus is very similar in character and depth to that of Turritella 

 accisa, Watson, and T. runcinata, Watson, being deeper than the lines 

 of growth indicate. It, however, almost amounts to a slit, and is 

 more definitely limited by strong raised threads on the whorls. This 

 is not, however, a typical species of Murcliisonia, but belongs to the 

 section Aclisoides, Don. 



No trace of an inner nacreous layer such as exists in Pleurotomaria 

 lias been observed either in the true Murchisonice, or in any of the 

 forms having a sinus associated with them. This is also the case 

 with the recent shells. Xo opercula have been discovered. In their 

 slender form they agree with Turritella, but the characteristic species 

 of that genus have the outer lip merely broadly sinuated instead 

 of having a deep sinus; the aperture is also rounded below instead of 

 being slightly channelled, and the columella is less produced. In the 

 section, or subgenus Torcula, Gray, however, the outer lip has a decided 

 sinus, but the base of the aperture differs in being excavated, and the 

 columella also is short instead of being produced. 



