KUNGL. SV. VET. AKADEMIENS HANDLINGAR. BAND 59. N:0 3- 13 



Such an investigation will enable us to test and explain the results arrived at 

 in the first chapter of this treatise. 



In the young specimens of Echinochnma the shell is quite different from that 

 of the adult one, as Fischer first stated in 1887 : »Le nucléus des Echinochama tranche 

 par sa coloration sur la teinte générale du test; il indique une coquille embryonnaire 

 équivalve, réguliére, ornée de cötes concentriques et ayant tout å fait 1'apparence 

 d'un Venerupis> (p. 1049). Jackson (1890, p. 370) verifies Fischer's observations 

 respecting the shape, colour and sculpture of the nepionic shell in Echinochama. 



Starting from Fischer's statements, Boehm (1891) made some additional ob- 

 servations on the young shell and from these drew some conclusions as to the rela- 

 tions of Chama. He says (p. 21): »Die Embryonalschale ist sehr ungleichseitig, mit 

 weit nach vorn geriickten Wirbeln, von erhabenen, ziemlich entfernt von einander 

 stehenden, concentrischen Lamellen bedeckt. Zwischen den letzteren beobachtet man 

 feine, concentrische Linien. Die Emb^onalschale von Echinochama arcinella ist frei 

 und gleichklappig. Sie weist demnach, wenn sonst man derselben eine grössere 

 Bedeutung zuerkennt, darauf hin, dass der Ursprung von Echinochama — auch Chama 

 und Diceras? — bei freien, gleichklappigen Pelecypoden zu suchen ist... Fischer 

 findet, dass jenes friihe Stadium in der Form an V enerupis erinner t. Ich wurde, wie 

 Steinmann, eher an Astarten aus der Gruppe Astarte Siuderi . . . denken. Auch ge- 

 hört V enerupis zu den Sinupalliaten, Astarte wie Echinochama zu den Integripalliaten.» 



Besides the above information, Dalt, in 1895 gives this brief diagnosis of his 

 super-family Chamacea: »Carditian forms specialized for a sessil habit with excep- 

 tionally spiral growth, and very unequal valves. Echinochama has a free nepionic 

 stage in which it has the form, hinge and other characters of Cardita» (p. 541). 



A detailed description of the free nepionic shell of Echinochama was given by 

 Dall in 1903 (p. 1395) vvhere he makes the following statements: »The hinge of the 

 left valve of the protoconch of Echinochama at about two millimetres length shows 

 a ligament with no conspicuous nymph, a single large cardinal slightly medially 

 grooved, and the rudiment of a second cardinal in front of the large one near the 

 dorsal börder. In a specimen 4.5 millimetres in length a callosity which may re- 

 present a third cardinal is developed on the ventral side of the nymph, and is on 

 its dorsal aspect distinctly crenulated. The large middle cardinal has become rela- 

 tively smaller and is now connected rather obscurely with the anterior cardinal, 

 which has elongated and become proportionally larger, while below it on the margin 

 of the hinge-plate a small corrugated thickening is perceptible. There is no trace 

 of an anterior lateral at any stage or in any species I have been able to study; if 

 present it has become obscured by the marginal crenulations. The posterior lateral 

 is, however, quite distinct in most cases in both valves. In the right valve at this 

 stage there are two simple, subequal, diverging cardinals, but no callosity on the 



nymph. The formula is -jx — i nio Tn' '^ s S row ^ 1 continues the teeth become tumid 



and corrugated, more or less irregular within the limits of the species, but in a ge- 

 neral way the attached valve has a ventral and one or two dorsal corrugated ridges 



