346 31R. H. LYDEKKER ON A LAHYRINTHODOKT SKULL 



that the two forms are generically identical. In describing the ver- 

 tebral skeleton of Ichthyerpetam, Prof. Huxley remarks that, in 

 comparison with the other Jarrow forms, "it is more piscitbrm"; 

 and in noticing the im])ression8 that appear to have been formed by 

 the ventral scutes, he observes that "the ventral surface of the 

 trunk presents numerous minute, more or less parallel ridges, 

 pointed at each end, and taking a general course obli(jucly down- 

 wards and forwards to the middle line." In describing PJiolklo- 

 (faster pisciformis, the Professor first of all states that he proposes 

 the name on account of its " lish-like form "; and in treating of the 

 ventral scutes or scales, observes that " they are seen to be some- 

 what oat-shaped," and are " so arranged as to form oblique series, 

 directed inwards and forwards, and meeting in the middle line." 

 When we recollect that the term "inwards" is precisely equivalent 

 to "downwards" in these cases, it will be apparent that the de- 

 scription of Ichtliyerpetum might be transferred to Pholi dor/a sfer, or 

 vice versa ; and I am thus strongly inclined to believe that the 

 latter is founded upon a larger species of the former. Additional 

 evidence in favour of this opinion is afforded by Prof. Huxley's 

 description of the skull of Pholidogaster, Here he observes that 

 " in front of the symphysis of the mandible, the under surface of 

 the prera axilla is visible, bearing the stumps of two teeth. These 

 teeth are situated at some distance (about 07 of an inch) from the 

 middle line, and pass outside the ramus of the mandible. They are 



conical, and round in transverse section The bases of the 



teeth are marked by strong longitudinal grooves." Remembering 

 that we have thi*ee in place of two premaxillary teeth remaining in 

 the skull of Icldliyerpetam hihernicum, this description will apply 

 word for word. 



Further evidence is, however, afforded by the skull of Bendrer- 

 •pttum^ where, according to Dr. Fritsch's figure *, the premaxillary 

 teeth are enlarged, separated by a diastema in the middle line, 

 deeply fluted at their base, and, judging from the outward inclina- 

 tion, apparently biting outside the mandible. 



In this connexion I find that Sir J, W. Dawson t long ago 

 pointed out that Ph olid o(j aster was closely allied to Dendrerpetum ; 

 and it is to my own mind not at all improbable that they may prove 

 to be identical. 



All these lines of evidence point, therefore, very clearly to the 

 conclusion that Ichthyeipetum and Pliolidogaster are identical, and 

 also suggest that they may be inseparable from Dendrerpetum. which 

 is the earliest of the three names. I refrain only with hesitation 

 from adopting the name Pliolidogaster in place of the later L.ldliyer- 

 petum ; but in view of the possibility that both these may prove to 

 be synonyms of Dendrerpetum., I have taken the course of referring 

 the specimen to the genus to which I absolutely know that it 

 belongs. 



I may avail myself of the opportunity of observing that any objec- 



* ' Fauna der Gaskolile,' vol. ii. pi. xlix. fig. 1. 



t 'Air-Breathers of th* Coal Period' (1863), pp. 22, 23. 



