Yol. 68.] LOWEE CAEBONirEROrS GASTEEOPODA. 297 



clusters, at other times larger and at some distance apart ; they 

 are circular, oval, or elongated. It is difficult to determine their 

 nature, for it is a question whether they constitute part of the 

 structure of the test ; or whether they are the scars left by the loss 

 of hairs from the epidermis ; or whether, again, they were formed 

 by some small boring parasite such as has been observed by Lind- 

 strom and Perner. The latter states that small perforations are 

 especially frequent in shells found in ' Eande ' E-g2 (Sil.), and he 

 thinks that they are probably due to parasitic organisms, perhaps 

 boring-sponges. When describing these in UmbotrocJius aspersus 

 (Barr.),^ and giving this view with regard to them, he states that 

 Barrande, on the contrary, considered them part of the ornamentation 

 of the test. The figures do not clearly show their exact character ; 

 but certainly the impression given is that they break through the 

 test of the shell, and hence must have originated later. I showed 

 the British specimens to Dr. J. G. Hinde, Mr. Gude, and Mr. Edgar 

 Smith, all of whom agree with me in thinking that these pittings 

 are due to irregularities in the growth of the shell -laminaB. 

 Mr. Gude says that they are not regular enough in their disposition 

 to have been caused by deciduous hairs, also hairs of this character 

 do not occur on marine shells. I have examined a number of 

 recent marine shells, Pleurotomaria adansoniana Crosse & Fischer 

 and PI. heyrichi Hilgendorf among them, and none of them exhibit 

 a similar structure. Dr. Hinde is of opinion that the pittings are 

 not such as could have been made by boring sponges. As evidence 

 in favour of their having been formed during the growth of the 

 shell, it may be mentioned that they do not break the lines of 

 growth, but either form depressions along these lines or else the 

 lines curve round them. Also they occur in shells from several 

 different localities, namely Kildare, Dublin, Lowick, and Weardale. 

 As the entire structure of the band is unknown, it is at present 

 impossible to ascertain the exact affinities of this genus. It 

 appears to come nearest to the Alatce group of Pleurotomaria, which 

 both Prof. Koken ^ and Prof. Perner ^ place in the genus Euompha- 

 lopterus Poemer."^ They consider that the crescents on the inner 

 band are not formed by the filling up of a slit in the outer lip as in 

 the true Pleurotomaria, but that they are the result of the breakage 

 of chambers formed during the growth of the superposed keel or 

 flange. Lindstrom,^ however, states that he has seen no evidence 

 of these inner chambers ; and he considers that, at the most, his 

 ' Alatce ' should merely constitute a subgenus, but certainly not a 

 distinct genus. I also have seen no specimens showing any signs 

 of internal chambers, and the lines of growth appear to me sugges- 

 tive of the former presence of a sinus of moderate depth in the outer 

 lip, over which the keel has been formed. This peculiar structure 



^•'Systeme Silurien du Centre de la Boheme ' pt. i, vol, iv, Gasteropodes r 

 par J. Perner, tome ii (1907) p. 240. 



'■* Neues Jahrb. Beilage-Band vi (1889) p. 439. '■^ Op. supra cit. p. 150. 



* ' Lethaea Geognostica ' 1876, pi. xiv, figs. 9 <r & 9 i. 

 5 K. Svensk. Vetensk.-Akad. Handl. n. s. vol. xix (1884) No. 6, p. 118. 



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