History of British animals - University of Guam Marine Laboratory

168 FISHES. CHONDROPT. Lamna.we call the Thresher, from the motion of its long fox-like tail, with which itstrikes or thrashes its larger and less agile enemy, the grampus, whenever itreaches the surface of the water to respire."Gen. XI. LAMNA. Porbeagle.— Branchial openings infront of the pectorals. Snout conical. Nostrils at thebase below.15. L. cornubica.— Teeth produced, slender, with two processeson each side at their base.Porbeagle, Borl. Corn. 265. tab. xxvi. f. 4. Penn. Brit. Zool. iii. 117.,and Beaumaris Shark, ib. 118. tab. xvii., and 2d edition Squalus cornubicus,Goodenough, Linn. Trans, iii. 80. tab. iii.Donovan, Brit.Fishes, tab. cviii.— S. Selanonus, Leach, Wern. Mem. ii. 64. tab. ii.f. 2—Not uncommon.Length from 5 to 9 feet. Colour bluish on the back, white on the belly.Snout projecting. Pectorals semilunar, the first dorsal, nearly immediatelyabove. Ventrals small. Posterior, dorsal, and anal fins small, opposite.Body contracted above and below at the setting on of the tail. Small tubercleson the lateral line. A ridge extending from the tail on each side thebody towards the middle. Tail semilunar, the upper lobe rather largest.This species is said to hunt its prey in companies. Its history as a Britishfish has become much involved in error. Pennant, by adding the Beaumarisshark as a new species, Avhen, with the single exception of its apparentlyshorter snout, its claims were insufficient, and by publishing an inaccurateengraving from an accurate drawing by the Reverend Hugh Davis, introducedthe confusion. Donovan advanced a step towards a reformation, by havingexamined the original drawing of Davis, and found it to correspond with thePorbeagle. The editor of the edition (1812) of Pennant's British Zoology,from a re-examination of the drawing of Mr Davis, asserts, that it " correspondsexactly with the original plate ;" yet, by a management which seemsinexplicable, the engraving in the new edition ischanged in many of its mostimportant features, so as to bear evident marks of differing from the formerplate, pronounced an accurate copy of the drawing. Dr Leach seems to havedescribed from a stuffed specimen of the Porbeagle his Squalus selanonius, supposingit to be Dr Walker's new species S. selanonius, and which he regards assimilar to the Squalus maximus, The Porbeagle isovoviviparous— It is occasionallycaught in the herring-nets.Squalus selanoneus This species was found by the late Dr Walker, inLochfyne, in Argyleshire (whence the name from Lochfyne, Smus selanoneusof Ptolemy), where it appears during the herring season. Stewart, in his" Elements of Nat. Hist. i.320.," inserts it in the section without the analfin, but with temporal orifices. In the description of this species in Dr Walker'sMS. Adversaria for 176!), p. 155., now before me, there is no noticetaken either of the anal fin or temporal orifices, so that I am inclined to inferthe absence of both. Should this be the case, it will claim to rank asa new genus, occupying a place between Charcharias and Lamna. I shallhere add the descriptionas it appears in the "original. Caput, maxilla subsequalis,superiore prominente, rostrata. Maxilla superior crassissima apicetruncata marginata, angulo superiori obtuso suberecto. Maxilla inferior angusta.Dentes numerosi acuti. Oculi super cantham oris positi sunt. Corpus,8-pedale oblongum, teretiusculum, cute aspera. Spiracula 5, anticobreviore, erecta, lineari-lunata margine : postico curvato. Tria spiraculapostica super pinnam pcctoralem positi sunt, duo altera ante pi'nnam pectora-